Information recording medium and recording/reproducing device

ABSTRACT

An information recording medium according to the present invention includes a track on which a data sequence including a plurality of recording marks and a plurality of spaces provided between the plurality of recording marks is recordable; and a recording condition recording area in which a recording condition for recording the data sequence on the track is recordable. Where a recording mark which is included in the data sequence and is to be formed on the track based on the recording condition is a first recording mark, when a length of the first recording mark is longer than a prescribed length, the recording condition is classified using a combination of the length of the first recording mark and a length of a first space located adjacently previous or subsequent to the first recording mark, and when the length of the first recording mark is equal to or shorter than the prescribed length, the recording condition is classified using a combination of the length of the first recording mark, the length of the first space, and a length of a second space not located adjacent to the first space and located adjacent to the first recording mark.

TECHNICAL FIELD

The present invention relates to an information recording medium and arecording/reproduction apparatus usable for optically recordinginformation, and specifically to an information recording medium and arecording/reproduction apparatus allowing recording conditions to beadjusted and thus realizing stable high density recording.

BACKGROUND ART

Various types of recordable information recording mediums have been putinto practice for recording video or audio data or storing personalcomputer data or the like. For example, CD mainly used for recordingaudio data or storing personal computer data and DVD used for recordingvideo data or storing personal computer data have increasingly spread.Recently, BD (Blu-ray Disc) on which high vision video of high imagequality including video of digital broadcasting can be recorded has beenput on the market.

The above-described information such as video, audio or personalcomputer data is recorded on an information recording medium as userdata. Specifically, the user data is provided with an error correctioncode and is modulated into a data sequence including recording marks andspaces having a prescribed range of length. The data sequence isrecorded on a track of the information recording medium using a lightbeam. From the information recorded on the information recording medium,an analog reproduction signal is generated. The analog reproductionsignal is specifically generated from reflected light which is obtainedby irradiating the track with a light beam and includes informationcorresponding to the data sequence, namely, the recording marks andspaces. From the reproduction signal, a data sequence, which is a binarysignal, is generated. The data sequence is decoded and then subjectedwith error correction. Thus, user data is obtained.

FIG. 1 shows various types of signals usable for forming a recordingmark on an information recording medium. FIG. 1, part (a), shows achannel clock signal of a cycle Tw, which acts as a reference signalused for generating recording data. FIG. 1, part (b), shows an NRZI (NonReturn to Zero Inverting) signal, which is a modulation code obtained bymodulating information to be recorded.

In the case of, for example, BD, the NRZI signal is obtained bymodulating information to be recorded using recording marks and spaceshaving a length of 2T (2×Tw) to 8T based on the cycle Tw as thereference. FIG. 1, part (b), shows a pattern of 2T mark-2T space-4T markas a general example of a part of the NRZI signal.

FIG. 1, parts (c) and (d), respectively show a recording pulse sequenceof recording laser generated based on the NRZI signal and a datasequence (recording mark sequence) formed on the information recordingmedium.

A recording mark of each length is formed by a recording pulse sequenceincluding at least a first pulse (also referred to as a “leadingpulse”). The recording mark further includes a last pulse and at leastone middle pulse located between the first pulse and the last pulse,depending on the length of the recording mark. A pulse width of thefirst pulse, Ttop, and a pulse width of the last pulse, Tlp, are eachset in accordance with the length of the recording mark. A pulse widthof the middle pulse, Tmp, is always set to the same length regardless ofthe length of the recording mark.

A level of the recording pulse sequence, namely, a laser intensity isclassified as a peak power Pp201 which provides a heating effectrequired for forming a recording mark, a bottom power Pb202 having acooling effect, a cooling power Pc203, and a space power Ps204 which isa recording power in the space. The peak power Pp201, the bottom powerPb202, the cooling power Pc203 and the space power Ps204 are set withrespect to an extinction level 205, detected when the laser light isturned off, as the reference level.

The bottom power Pb202 and the cooling power Pc203 are generally set toan equivalent recording power. However, the cooling power Pc203 may beset to a different value from the bottom power Pb202 in order to adjustthe heat amount at an end of a recording mark. The space power Ps204 isgenerally set to a low recording power (for example, a recording powerequivalent to a reproduction power or the bottom power) because it isnot necessary to form a recording mark in a space. However, for arewritable optical disc (for example, DVD-RAM or BD-RE), the existingrecording mark needs to be erased to create a space. For a write onceoptical disc (for example, DVD-R or BD-R), a preheating power forcreating the next recording mark may be occasionally provided. For thesereasons, the space power Ps204 may be set to a relatively high recordingpower. Even in this case, the space power Ps204 is never set to be ahigher value than that of the peak power Pp201.

The recording mark formed by irradiation with laser of a prescribedpower depends on the characteristics of each information recording layerof the information recording medium. Therefore, the informationrecording medium has recorded thereon laser emission conditions forrecording such as the laser power value, the pulse width and the like ofthe recording pulse sequence suitable to the information recordingmedium. By appropriately reproducing the laser power and the pulse widthof the recording pulses recorded in the information recording medium andirradiating the information recording medium with appropriate laserlight, a recording mark sequence can be formed.

However, the characteristics of each information recording layer of theinformation recording medium and the laser emission characteristics ofthe recording apparatus are varied for an individual informationrecording medium or an individual recording apparatus. The influence ofheat is also varied in accordance with the environment of use. Thermalinterference may be caused from an adjacent recording mark. For thesereasons, at least each time a new information recording medium ismounted, the recording apparatus generally performs test recording toevaluate the obtained reproduction signal and to fine-tune the pulseshape of the recording laser based on the evaluation results, so thatcorrect recording marks are formed. For example, for each length ofrecording mark, recording start position offset dTtop for adjusting thestart position of the recording mark and the recording end positionoffset dTs for adjusting the end position of the recording mark are set,and these offset values are adjusted at the time of test recording.

The recording pulses included in the recording pulse sequence may have amono-pulse waveform, an L-shaped pulse waveform or a castle-type pulsewaveform as shown in FIG. 2, parts (a), (b) and (c) in addition to theabove-described multi-pulse waveform. In general, with the mono-pulsewaveform, as the recording mark is longer, the amount of accumulatedheat increases. With the L-shaped pulse waveform, as the recording markis longer, the amount of accumulated heat decreases. With thecastle-type pulse waveform, the heat amount at the end of the recordingmark is adjusted. With the multi-pulse waveform, the amount ofaccumulated heat is constant regardless of the length of the recordingmark. In consideration of these, an appropriate waveform is selected inaccordance with the layer characteristics of the information recordinglayer of the information recording medium, especially thecharacteristics of the accumulated heat.

Recently, as the display precision of video is raised, an informationrecording medium having a larger capacity is desired. In order toincrease the recording density of the information recording medium, therecording marks used for recording information need to be smaller.However, as the recording marks become smaller, the shortest recordingmark length is close to the limit of the optical resolution, and so theincrease of the inter-symbol interference and the deterioration of theSNR (signal-to-noise ratio) become conspicuous. As a result, the leadingedge or the trailing edge of the recording mark cannot be correctlydetected, which makes it difficult to correctly decode the recordedinformation from the reproduction signal.

For this reason, for reproducing information from an informationrecording medium on which information is recorded with small recordingmarks, it has become popular to process the reproduction signal using aPRML (Partial Response Maximum Likelihood) system or the like. The PRMLsystem is a combination technology of partial response (PR) and maximumlikelihood decoding (ML), and estimates waveforms of the reproductionsignal when known inter-symbol interference occurs and selects a mostlikely signal sequence from the estimated waveforms.

As the recording marks become small, thermal interference occurs.Specifically, the heat at the end of the recording mark is conductedthrough the space and influences the temperature rise at the start ofthe subsequent recording mark, or the heat at the start of thesubsequent recording mark influences the cooling process at the end ofthe previous recording mark. When such thermal interference occurs,space compensation needs to be provided by test recording. Spacecompensation is to change the recording parameters (for example, dTtop)of the recording pulse in accordance with the length of the previousspace or the subsequent space.

Patent Documents No. 1 and No. 2, for example, each describe aconventional method for controlling the recording pulse in considerationof the influence of the inter-symbol interference or thermalinterference.

According to the method disclosed in Patent Document No. 1, a correctbit stream obtained by correct demodulation and an error bit stream witha maximum likelihood of error, which is generated as a result of one bitof the correct bit stream being shifted, are used to calculate anEuclidian distance between the reproduction signal and each of both bitstreams. Thus, a reproduction signal adaptively equalized is evaluated,thereby detecting an edge shift direction and an edge shift amount ofeach pattern. Adaptive recording parameters classified by the length ofthe recording mark to be formed and the length of the space immediatelyprevious or subsequent thereto are optimized in accordance with the edgeshift direction and the edge shift amount corresponding to each pattern.

According to Patent Document No. 2, for an edge at which one bit isshifted from a correct bit stream and an incorrect bit stream, adifference between the amplitude value of an adaptively equalizedreproduction signal and an expected amplitude value calculated in eachstream is quantified. Thus, an edge shift direction and an edge shiftamount are detected. Like in Patent Document No. 1, the adaptiverecording parameters organized in a table by the length of the mark andthe length of the space immediately previous or subsequent thereto areoptimized in accordance with the edge shift direction and the edge shiftamount corresponding to each pattern.

In Patent Documents No. 1 and No. 2, a reproduction signal is processedby a PR1221ML system. The recording pulse control disclosed in PatentDocument No. 1 will be further described with reference to FIG. 3.

Information read from an information recording medium 1 is generated asan analog reproduction signal by an optical head 2. The analogreproduction signal is amplified and AC-coupled by a preamplifier 3, andthen input to an AGC section 4. The AGC section 4 adjusts the amplitudesuch that the output from a waveform equalizer 5 on a later stage has aconstant amplitude. The amplitude-adjusted analog reproduction signal iswaveform-shaped by the waveform equalizer 5 and input to an A/Dconversion section 6. The A/D conversion section 6 samples the analogreproduction signal in synchronization with a reproduction clock outputfrom a PLL section 7. The PLL section 7 extracts the reproduction clockfrom a digital reproduction signal obtained by the sampling performed bythe A/D conversion section 6.

The digital reproduction signal generated by the sampling performed bythe A/D conversion section 6 is input to a PR equalization section 8.The PR equalization section 8 adjusts the frequency of the digitalreproduction signal such that the frequency characteristic of thedigital reproduction signal at the time of recording/reproduction is thecharacteristic assumed by a maximum likelihood decoding section 9 (forexample, PR(1,2,2,1) equalization characteristic). The maximumlikelihood decoding section 9 performs maximum likelihood decoding onthe waveform-shaped digital reproduction signal output from the PRequalization section 8 to generate a binary signal. The reproductionsignal processing technology provided by combining the PR equalizationsection 8 and the maximum likelihood decoding section 9 is the PRMLsystem.

An edge shift detection section 10 receives the waveform-shaped digitalreproduction signal output from the PR equalization section 8 and thebinary signal output from the maximum likelihood decoding section 9. Theedge shift detection section 10 distinguishes a state transfer from thebinary signal, and finds the reliability of the decoding result from thedistinguishing result and the branch metric. The edge shift detectionsection 10 also assigns the reliability for each of leadingedge/trailing edge patterns of recording marks based on the binarysignal and finds a shift of a recording compensation parameter from theoptimal value (hereinafter, the shift will be referred to as the “edgeshift”).

Test recording is performed using a data sequence having a prescribedrecording pattern. An information recording control section 15 changes arecording parameter, the setting change of which is possible, inconformity to the information indicating that the setting change of therecording parameter is determined as being required based on the edgeshift amount detected for each pattern. The recording parameters, thesetting of which is changeable, are predetermined. Such recordingparameters include, for example, the recording start position offsetdTtop regarding the leading edge of a recording mark and the recordingend position offset dTs regarding the trailing edge of a recording mark.The information recording control section 15 changes the recordingparameter in accordance with the table of the recording parameters shownin FIG. 4. FIG. 4 shows recording parameters regarding the leading edgeclassified by the length of the recording mark and the length of thespace immediately previous thereto, and recording parameters regardingthe trailing edge classified by the length of the recording mark and thelength of the space immediately subsequent thereto.

In FIG. 4, the symbols of recording mark M′(i), immediately previousspace S(i−1) and immediately subsequent space S(i+1) are used in thetime series of recording marks and spaces shown in FIG. 5. Symbol Mrepresents a recording mark and symbol S represents a space. A positionin the time series of an arbitrary recording mark or space isrepresented using symbol i.

The recording mark corresponding to the recording parameter shown inFIG. 4 is represented by M(i). As shown in FIG. 5, a space immediatelyprevious to the recording mark M(i) is S(i−1), a recording mark furtherimmediately previous is M(i−2), and a space still further immediatelyprevious is S(i−3). A space immediately subsequent to the recording markM(i) is S(i+1), a recording mark further immediately subsequent isM(i+2), and a space still further immediately subsequent is S(i+3).

The leading edge is located between the recording mark M(i) and theimmediately previous space S(i−1). As shown in FIG. 4, the value ofdTtop is classified by the pattern in accordance with a combination ofthe lengths thereof. For example, in the case where the length of theimmediately previous space is 3T and the length of the recording mark is4T, the pattern 3Ts4Tm is used. The trailing edge is located between therecording mark M(i) and the immediately subsequent space S(i+1). Asshown in FIG. 4, the value of dTs is classified by the pattern inaccordance with a combination of the lengths thereof. For example, inthe case where the length of the recording mark is 3T and the length ofthe immediately subsequent space is 2T, the pattern 3Tm2Ts is used. Asshown in FIG. 4, there are a total of 32 recording parameter valuesregarding the leading edge and the trailing edge.

In order to adjust, for example, the leading edge of a recording mark of4T having an immediately previous space of 3T, the information recordingcontrol section 15 changes a recording parameter of 3Ts4Tm (for example,dTop). In order to adjust, for example, the trailing edge of a recordingmark of 3T having an immediately subsequent space of 2T, the informationrecording control section 15 changes a recording parameter of 3Tm2Ts(for example, dTs).

A recording pattern generation section 11 generates an NRZI signal whichis modulated by input information to be recorded. A recordingcompensation section 12 generates a recording pulse sequence inaccordance with the NRZI signal based on the recording parameter changedby the information recording control section 15. A recording powersetting section 14 sets recording powers including the peak power Pp,the bottom power Pbw and the like. A laser driving section 13 controlsthe laser light emitting operation of the optical head 2 in accordancewith the recording pulse sequence and the recording powers set by therecording power setting section 14.

In this manner, test recording is performed on the information recordingmedium 1, and a recording pulse shape is controlled so as to decreasethe edge shift amount. Thus, by the recording control method using thePRML system and space compensation of recording parameters, moreappropriate recording marks and spaces can be formed.

Citation List Patent Document

Patent Document No. 1: Japanese Laid-Open Patent Publication No.2004-335079

Patent Document No. 2: Japanese Laid-Open Patent Publication No.2008-112509

SUMMARY OF INVENTION Technical Problem

As the recording density of information recording mediums is moreimproved, the problems of the inter-symbol interference and SNRdeterioration become more serious. This makes it necessary to process areproduction signal obtained from the information recording medium by ahigher order PRML system.

In this case, in order to appropriately reproduce the informationrecorded on the information recording medium by the higher order PRMLsystem, it is necessary to perform test recording to adjust the edgeposition of the recording mark at higher precision and adjust therecording conditions to reduce the error rate at the time of signalreproduction.

The present invention has an object of providing an informationrecording medium and a recording/reproduction apparatus allowingrecording conditions to be adjusted such that the probability of errorgeneration at the time of maximum likelihood decoding is minimized inconsideration of a high order PRML system and thus realizing stable highdensity recording. More specifically, the present invention has anobject of reducing the error rate of recording information in highdensity recording and realizing a more stable recording/reproductionsystem.

Solution to Problem

An information recording medium according to the present inventionincludes a track on which a data sequence including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks is recordable; and a recording condition recordingarea in which a recording condition for recording the data sequence onthe track is recordable. Where a recording mark which is included in thedata sequence and is to be formed on the track based on the recordingcondition is a first recording mark, when a length of the firstrecording mark is longer than a prescribed length, the recordingcondition is classified using a combination of the length of the firstrecording mark and a length of a first space located adjacently previousor subsequent to the first recording mark, and when the length of thefirst recording mark is equal to or shorter than the prescribed length,the recording condition is classified using a combination of the lengthof the first recording mark, the length of the first space, and a lengthof a second space not located adjacent to the first space and locatedadjacent to the first recording mark.

In a preferable embodiment, the prescribed length is a length of ashortest recording mark in the data sequence.

In a preferable embodiment, in the classification performed using acombination of the length of the first recording mark, the length of thefirst space, and the length of the second space, the number of types ofthe lengths of the first space is larger than the number of types of thelengths of the second space.

In a preferable embodiment, the recording condition is a parameter foradjusting a position of a leading edge of the first recording mark, andthe first space is adjacently previous to the first recording mark.

In a preferable embodiment, the recording condition is a parameter foradjusting a position of a trailing edge of the first recording mark, andthe first space is adjacently subsequent to the first recording mark.

A reproduction apparatus according to the present invention is areproduction apparatus for reproducing information from the informationrecording medium defined by any of the above. The information recordingmedium includes a PIC area for storing disc information on theinformation recording medium. The reproduction apparatus includes areproduction signal processing section for executing at least one ofirradiation of the PIC area with laser light to reproduce the discinformation and irradiation of the track with the laser light toreproduce information which is recorded based on the recordingcondition.

A recording apparatus according to the present invention is a recordingapparatus for recording a data sequence, including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks, on an information recording medium based on arecording condition recorded on the information recording medium. Therecording apparatus includes a reproduction signal processing sectionfor irradiating the information recording medium with laser light toreproduce the recording condition; and a recording control section forrecording information on the information recording medium based on therecording condition. Where a recording mark which is included in thedata sequence and is to be formed on the track based on the recordingcondition is a first recording mark, when a length of the firstrecording mark is longer than a prescribed length, the recordingcondition is classified using a combination of the length of the firstrecording mark and a length of a first space located adjacently previousor subsequent to the first recording mark; and when the length of thefirst recording mark is equal to or shorter than the prescribed length,the recording condition is classified using a combination of the lengthof the first recording mark, the length of the first space, and a lengthof a second space not located adjacent to the first space and locatedadjacent to the first recording mark.

An evaluation apparatus according to the present invention is anevaluation apparatus for evaluating an information recording mediumhaving a recording parameter recorded thereon, the recording parameterbeing for recording a data sequence including a plurality of recordingmarks and a plurality of spaces provided between the plurality ofrecording marks. Where a recording mark which is included in the datasequence and is to be formed on the track based on the recordingcondition is a first recording mark, when a length of the firstrecording mark is longer than a prescribed length, the recordingparameter is classified using a combination of the length of the firstrecording mark and a length of a first space located adjacently previousor subsequent to the first recording mark, and when the length of thefirst recording mark is equal to or shorter than the prescribed length,the recording parameter is classified using a combination of the lengthof the first recording mark, the length of the first space, and a lengthof a second space not located adjacent to the first space and locatedadjacent to the first recording mark. The evaluation apparatus comprisesa reproduction signal processing section for generating a digital signalfrom a signal reproduced from the information recording medium using aPRML signal processing system, decoding a binary signal from the digitalsignal, calculating a differential metric, which is a difference of thereproduction signal from each of a most likely first state transitionsequence and a most likely second state transition sequence, from thebinary signal and detecting each differential metric as an edge shift,and determining whether or not the information recording medium fulfillsa prescribed quality based on the edge shifts.

A recording/reproduction apparatus according to the present inventionperforms at least one of reproduction from and recording on aninformation recording medium determined by the evaluation apparatus ofclaim 8 as fulfilling the prescribed quality.

An information recording medium according to the present invention is aninformation recording medium which includes a recording conditionrecording area in which recording conditions are recordable, and onwhich a data sequence including a plurality of recording marks and aplurality of spaces provided between the plurality of recording marks isrecordable. The recording conditions are classified by a length of therecording mark. Where the recording conditions are each a parameter foradjusting a position of a leading edge of the recording mark, at leastone of the recording conditions classified by the length of therecording mark is further classified into two in accordance with whethera length of a space adjacently subsequent to the recording mark is equalto or shorter than a prescribed length or longer than the prescribedlength. Where the recording conditions are each a parameter foradjusting a position of a trailing edge of the recording mark, at leastone of the recording conditions classified by the length of therecording mark is further classified into two in accordance with whethera length of a space adjacently previous to the recording mark is equalto or shorter than the prescribed length or longer than the prescribedlength.

A reproduction apparatus according to the present invention is areproduction apparatus for reproducing information from the informationrecording medium. The information recording medium includes a PIC areafor storing disc information on the information recording medium. Thereproduction apparatus includes a reproduction signal processing sectionfor executing at least one of irradiation of the PIC area with laserlight to reproduce the disc information and irradiation of the trackwith the laser light to reproduce information which is recorded based onthe recording condition.

A recording apparatus according to the present invention is a recordingapparatus for recording a data sequence, including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks, on an information recording medium based on arecording condition recorded on the information recording medium. Therecording apparatus includes a reproduction signal processing sectionfor irradiating the information recording medium with laser light toreproduce the recording condition; and a recording control section forrecording information on the information recording medium based on therecording condition. The recording conditions are classified by a lengthof the recording mark. Where the recording conditions are each aparameter for adjusting a position of a leading edge of the recordingmark, at least one of the recording conditions classified by the lengthof the recording mark is further classified into two in accordance withwhether a length of a space adjacently subsequent to the recording markis equal to or shorter than a prescribed length or longer than theprescribed length. Where the recording conditions are each a parameterfor adjusting a position of a trailing edge of the recording mark, atleast one of the recording conditions classified by the length of therecording mark is further classified into two in accordance with whethera length of a space adjacently previous to the recording mark is equalto or shorter than the prescribed length or longer than the prescribedlength.

An evaluation apparatus according to the present invention is anevaluation apparatus for evaluating an information recording mediumhaving recording conditions recorded thereon, the recording conditionsbeing for recording a data sequence including a plurality of recordingmarks and a plurality of spaces provided between the plurality ofrecording marks. The recording conditions are classified by a length ofthe recording mark. Where recording conditions are each a parameter foradjusting a position of a leading edge of the recording mark, at leastone of the recording conditions classified by the length of therecording mark is further classified into two in accordance with whethera length of a space adjacently subsequent to the recording mark is equalto or shorter than a prescribed length or longer than the prescribedlength. Where the recording conditions are each a parameter foradjusting a position of a trailing edge of the recording mark, at leastone of the recording conditions classified by the length of therecording mark is further classified into two in accordance with whethera length of a space adjacently previous to the recording mark is equalto or shorter than the prescribed length or longer than the prescribedlength. The evaluation apparatus includes a reproduction signalprocessing section for generating a digital signal from a signalreproduced from the information recording medium using a PRML signalprocessing system, decoding a binary signal from the digital signal,calculating a differential metric, which is a difference of thereproduction signal from each of a most likely first state transitionsequence and a most likely second state transition sequence, from thebinary signal and detecting each differential metric as an edge shift,and determining whether or not the information recording medium fulfillsa prescribed quality based on the edge shifts.

A recording/reproduction apparatus according to the present inventionperforms at least one of reproduction from and recording on aninformation recording medium determined by the above evaluationapparatus as fulfilling the prescribed quality.

An information recording medium according to the present inventionincludes a track on which a data sequence including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks is recordable; and at least one of a PIC area inwhich a recording condition for recording the data sequence on the trackis recorded, and wobbling of the track by which the recording conditionis recorded. The recording condition includes a parameter for adjustinga position of a trailing end of a cooling pulse in a recording pulsewaveform for forming the recording mark. The parameter is classifiedusing a combination of a length of the recording mark and a length of aspace located adjacently previous or subsequent to the recording mark.

A reproduction apparatus according to the present invention is areproduction apparatus for reproducing information from the aboveinformation recording medium. The reproduction apparatus includes areproduction signal processing section for executing at least one ofirradiation of the PIC area with laser light to reproduce discinformation and irradiation of the track with the laser light toreproduce information which is recorded based on the recordingcondition.

A recording apparatus according to the present invention is a recordingapparatus for recording a data sequence, including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks, on an information recording medium based on arecording condition recorded on the information recording medium. Therecording apparatus includes a reproduction signal processing sectionfor irradiating the information recording medium with laser light toreproduce the recording condition; and a recording control section forrecording information on the information recording medium based on therecording condition. The recording condition includes a parameter foradjusting a position of a trailing end of a cooling pulse in a recordingpulse waveform for forming the recording mark. The parameter isclassified using a combination of a length of the recording mark and alength of a space located adjacently previous or subsequent to therecording mark.

An evaluation apparatus according to the present invention is anevaluation apparatus for evaluating an information recording mediumhaving a recording parameter recorded thereon, the recording parameterbeing for recording a data sequence including a plurality of recordingmarks and a plurality of spaces provided between the plurality ofrecording marks. The recording condition includes a parameter foradjusting a position of a trailing end of a cooling pulse in a recordingpulse waveform for forming the recording mark. The parameter isclassified using a combination of a length of the recording mark and alength of a space located adjacently previous or subsequent to therecording mark. The evaluation apparatus comprises a reproduction signalprocessing section for generating a digital signal from a signalreproduced from the information recording medium using a PRML signalprocessing system, decoding a binary signal from the digital signal,calculating a differential metric, which is a difference of thereproduction signal from each of a most likely first state transitionsequence and a most likely second state transition sequence, from thebinary signal and detecting each differential metric as an edge shift,and determining whether or not the information recording medium fulfillsa prescribed quality based on the edge shifts.

A recording/reproduction apparatus according to the present inventionperforms at least one of reproduction from and recording on aninformation recording medium determined by the above evaluationapparatus as fulfilling the prescribed quality.

A recording control apparatus, according to the present invention, forrecording information on an information recording medium includes arecording compensation parameter determination section for classifyingrecording conditions by data pattern, including at least one recordingmark and at least one space, of a data sequence to be recorded. Theclassification of the recording conditions by data pattern is performedusing a combination of the length of a first recording mark included inthe data sequence and the length of a first space located adjacentlyprevious or subsequent to the first recording mark, and then furtherperformed using the length of a second recording mark which is notlocated adjacent to the first recording mark and is located adjacent tothe first space.

In a preferable embodiment, the classification using the length of thesecond recording mark is performed only when the length of the firstspace is equal to or less than a prescribed length.

In a preferable embodiment, the classification by data pattern isfurther performed using the length of a second space which is notlocated adjacent to the first recording mark or the first space and islocated adjacent to the second recording mark.

In a preferable embodiment, the classification using the length of thesecond space is performed only when the length of the second recordingmark is equal to or less than the prescribed length.

In a preferable embodiment, the prescribed length is the shortest lengthin the data sequence.

A recording control apparatus, according to the present invention, forrecording information on an information recording medium includes arecording compensation parameter determination section for classifyingrecording conditions by data pattern, including at least one recordingmark and at least one space, of a data sequence to be recorded. Theclassification of the recording conditions by data pattern is performedusing a combination of the length of a first recording mark included inthe data sequence and the length of a first space located adjacentlyprevious or subsequent to the first recording mark, and then furtherperformed using the length of a second space which is not locatedadjacent to the first space and is located adjacent to the firstrecording mark.

In a preferable embodiment, the classification using the length of thesecond space is performed only when the length of the first recordingmark is equal to or less than the prescribed length.

In a preferable embodiment, the classification by data pattern isfurther performed using the length of a second recording mark which isnot located adjacent to the first recording mark or the first space andis located adjacent to the second space.

In a preferable embodiment, the classification using the length of thesecond recording mark is performed only when the length of the secondspace is equal to or less than the prescribed length.

In a preferable embodiment, the prescribed length is the shortest lengthin the data sequence.

A recording control method according to the present invention is forrecording information on an information recording medium. By therecording control method, recording conditions are classified by datapattern, including at least one recording mark and at least one space,of a data sequence to be recorded. The classification of the recordingconditions by data pattern is performed using a combination of thelength of a first recording mark included in the data sequence and thelength of a first space located adjacently previous or subsequent to thefirst recording mark, and then further performed using the length of asecond recording mark which is not located adjacent to the firstrecording mark and is located adjacent to the first space.

In a preferable embodiment, the classification using the length of thesecond recording mark is performed only when the length of the firstspace is equal to or less than a prescribed length.

In a preferable embodiment, the classification by data pattern isfurther performed using the length of a second space which is notlocated adjacent to the first recording mark or the first space and islocated adjacent to the second recording mark.

In a preferable embodiment, the classification using the length of thesecond space is performed only when the length of the second recordingmark is equal to or less than the prescribed length.

In a preferable embodiment, the prescribed length is the shortest lengthin the data sequence.

A recording control method according to the present invention is forrecording information on an information recording medium. By therecording control method, recording conditions are classified by datapattern, including at least one recording mark and at least one space,of a data sequence to be recorded. The classification of the recordingconditions by data pattern is performed using a combination of thelength of a first recording mark included in the data sequence and thelength of a first space located adjacently previous or subsequent to thefirst recording mark, and then further performed using the length of asecond space which is not located adjacent to the first space and islocated adjacent to the first recording mark.

In a preferable embodiment, the classification using the length of thesecond space is performed only when the length of the first recordingmark is equal to or less than the prescribed length.

In a preferable embodiment, the classification by data pattern isfurther performed using the length of a second recording mark which isnot located adjacent to the first recording mark or the first space andis located adjacent to the second space.

In a preferable embodiment, the classification using the length of thesecond recording mark is performed only when the length of the secondspace is equal to or less than the prescribed length.

In a preferable embodiment, the prescribed length is the shortest lengthin the data sequence.

A recording/reproduction apparatus according to the present inventionincludes a reproduction signal processing section for generating adigital signal and decoding the digital signal into a binary signal,from a signal reproduced from an information recording medium using aPRML signal processing system; and a recording control section foradjusting a recording parameter for recording information on theinformation recording medium based on the digital signal and the binarysignal and recording the information on the information recordingmedium. The recording control section includes a recording compensationparameter determination section for classifying recording conditions bydata pattern, including at least one recording mark and at least onespace, of a data sequence to be recorded. The classification of therecording conditions by data pattern is performed using a combination ofthe length of a first recording mark included in the data sequence andthe length of a first space located adjacently previous or subsequent tothe first recording mark, and then further performed using the length ofa second recording mark which is not located adjacent to the firstrecording mark and is located adjacent to the first space.

A recording/reproduction apparatus according to the present inventionincludes a reproduction signal processing section for generating adigital signal and decoding the digital signal into a binary signal,from a signal reproduced from an information recording medium using aPRML signal processing system; and a recording control section foradjusting a recording parameter for recording information on theinformation recording medium based on the digital signal and the binarysignal and recording the information on the information recordingmedium. The recording control section includes a recording compensationparameter determination section for classifying recording conditions bydata pattern, including at least one recording mark and at least onespace, of a data sequence to be recorded. The classification of therecording conditions by data pattern is performed using a combination ofthe length of a first recording mark included in the data sequence andthe length of a first space located adjacently previous or subsequent tothe first recording mark, and then further performed using the length ofa second space which is not located adjacent to the first space and islocated adjacent to the first recording mark.

In a preferable embodiment, the reproduction signal processing sectionincludes an edge shift detection section for calculating, from thebinary signal, a differential metric which is a difference of areproduction signal from a most likely first state transition sequenceand a most likely second state transition sequence, assigning thedifferential metric to each of leading edge/trailing edge patterns ofthe recording marks based on the binary signal, and finding an edgeshift of the recording parameter from an optimal value for each pattern.The recording parameter is adjusted such that the edge shift approachesa prescribed target value.

In a preferable embodiment, the classification by data pattern obtainedin the recording compensation parameter determination step and theclassification by pattern obtained in the edge shift detection step arethe same.

A recording/reproduction method according to the present inventionincludes a reproduction signal processing step of generating a digitalsignal and decoding the digital signal into a binary signal, from asignal reproduced from an information recording medium using a PRMLsignal processing system; and a recording control step of adjusting arecording parameter for recording information on the informationrecording medium based on the digital signal and the binary signal andrecording the information on the information recording medium. Therecording control step includes a recording compensation parameterdetermination step of classifying recording conditions by data pattern,including at least one recording mark and at least one space, of a datasequence to be recorded, the data pattern. The classification of therecording conditions by data pattern is performed using a combination ofthe length of a first recording mark included in the data sequence andthe length of a first space located adjacently previous or subsequent tothe first recording mark, and then further performed using the length ofa second recording mark which is not located adjacent to the firstrecording mark and is located adjacent to the first space.

A recording/reproduction method according to the present inventionincludes a reproduction signal processing step of generating a digitalsignal and decoding the digital signal into a binary signal, from asignal reproduced from an information recording medium using a PRMLsignal processing system; and a recording control step of adjusting arecording parameter for recording information on the informationrecording medium based on the digital signal and the binary signal andrecording the information on the information recording medium. Therecording control step includes a recording compensation parameterdetermination step of classifying recording conditions by data pattern,including at least one recording mark and at least one space, of a datasequence to be recorded, the data pattern. The classification of therecording conditions by data pattern is performed using a combination ofthe length of a first recording mark included in the data sequence andthe length of a first space located adjacently previous or subsequent tothe first recording mark, and then further performed using the length ofa second space which is not located adjacent to the first space and islocated adjacent to the first recording mark.

In a preferable embodiment, the reproduction signal processing stepincludes an edge shift detection step of calculating, from the binarysignal, a differential metric which is a difference of a reproductionsignal from a most likely first state transition sequence and a mostlikely second state transition sequence, assigning the differentialmetric to each of leading edge/trailing edge patterns of the recordingmarks based on the binary signal, and finding an edge shift of therecording parameter from an optimal value for each pattern. Therecording parameter is adjusted such that the edge shift approaches aprescribed target value.

In a preferable embodiment, the classification by data pattern obtainedin the recording compensation parameter determination step and theclassification by pattern obtained in the edge shift detection step arethe same.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a recording condition for recordinga data sequence on a track is classified using a combination of a lengthof a recording mark as a target of the recording parameter adjustmentand a length of a space adjacently previous or subsequent thereto. Whenthe length of the recording mark as the target of the recordingparameter adjustment is equal to or shorter than a prescribed length,the recording condition is further classified also using a length of aspace adjacently subsequent or previous to the above adjacent space.Therefore, even where the size of the recording mark is extremelydecreased and the recording density of the information recording mediumbecomes high, a recording mark having an appropriate shape can berecorded at an appropriate position at higher precision in considerationof the influence of the heat generated when an adjacent recording markis formed.

Accordingly, by adjusting the recording condition in accordance with thepresent invention, the error rate of recorded information can be reducedin high density recording which requires a high-order PRML system andthus a more stable recording/reproduction system can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows recording pulse waveforms and recording power for forming adata sequence including a recording mark and a space.

FIG. 2 shows examples of recording pulse shapes.

FIG. 3 shows a conventional recording control apparatus.

FIG. 4 shows conventional recording parameter tables.

FIG. 5 shows a time series of recording marks and spaces.

FIG. 6 shows a state transition rule defined by the RLL(1,7) recordingcode and the equalization system PR(1,2,2,2,1) according to anembodiment of the present invention.

FIG. 7 is a trellis diagram corresponding to the state transition ruleshown in FIG. 6.

FIG. 8 shows state transition sequence patterns by PR12221ML.

FIG. 9 shows state transition sequence patterns by PR12221ML.

FIG. 10 shows state transition sequence patterns by PR12221ML.

FIG. 11 shows an example of PR equalization ideal waveforms shown inFIG. 8.

FIG. 12 shows an example of PR equalization ideal waveforms shown inFIG. 9.

FIG. 13 shows an example of PR equalization ideal waveforms shown inFIG. 10.

FIG. 14 shows a signal evaluation apparatus using the PR12221ML system.

FIG. 15 shows classification into detailed patterns of differentialmetrics having a 14-detection pattern by PR(1,2,2,2,1)ML.

FIG. 16 shows classification into detailed patterns of differentialmetrics having a 12A-detection pattern by PR(1,2,2,2,1)ML.

FIG. 17 shows classification into detailed patterns of differentialmetrics having a 12B-detection pattern by PR(1,2,2,2,1)ML.

FIG. 18 shows a pattern table of recording parameters according to anembodiment of the present invention.

FIG. 19 shows recording pulses corresponding to the pattern table shownin FIG. 18.

FIG. 20 shows another pattern table of recording parameters according toan embodiment of the present invention.

FIG. 21 shows recording pulses corresponding to the pattern table shownin FIG. 20.

FIG. 22 shows still another pattern table of recording parametersaccording to an embodiment of the present invention.

FIG. 23 shows recording pulses corresponding to the pattern table shownin FIG. 22.

FIG. 24 shows still another pattern table of recording parametersaccording to an embodiment of the present invention.

FIG. 25 shows recording pulses corresponding to the pattern table shownin FIG. 24.

FIG. 26 shows still another pattern table of recording parametersaccording to an embodiment of the present invention.

FIG. 27 shows recording pulses corresponding to the pattern table shownin FIG. 26.

FIG. 28 shows still another pattern table of recording parametersaccording to an embodiment of the present invention.

FIG. 29 shows recording pulses corresponding to the pattern table shownin FIG. 28.

FIG. 30 shows still another pattern table of recording parametersaccording to an embodiment of the present invention.

FIG. 31 shows recording pulses corresponding to the pattern table shownin FIG. 30.

FIG. 32 shows still another pattern table of recording parametersaccording to an embodiment of the present invention.

FIG. 33 shows recording pulses corresponding to the pattern table shownin FIG. 32.

FIG. 34 is a block diagram showing an information recording/reproductionapparatus according to an embodiment of the present invention.

FIG. 35 shows an example of recording pulse waveforms usable in thepresent invention.

FIG. 36 shows another example of recording pulse waveforms usable in thepresent invention.

FIG. 37 shows still another example of recording pulse waveforms usablein the present invention.

FIG. 38 is a schematic view showing an example of a structure of aninformation recording medium to which the present invention isapplicable.

FIG. 39 is a schematic view showing a structure of a single layerinformation recording medium.

FIG. 40 is a schematic view showing a structure of a two-layerinformation recording medium.

FIG. 41 is a schematic view showing a structure of a three-layerinformation recording medium.

FIG. 42 is a schematic view showing a structure of a four-layerinformation recording medium.

FIG. 43 is a schematic view showing a physical structure of aninformation recording medium.

FIG. 44 is a schematic view showing an optical spot of a laser beam andmarks recorded on a track.

FIG. 45 is another schematic view showing an optical spot of a laserbeam and marks recorded on a track.

FIG. 46 shows how a mark sequence recorded on a track is irradiated witha light beam.

FIG. 47 is a graph showing the relationship between the OTF and theshortest recording mark.

FIG. 48 is another graph showing the relationship between the OTF andthe shortest recording mark.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the figures.

According to the present invention, in order to increase the recordingdensity of an information recording medium, the scanning speed with thelaser beam, namely, the linear velocity is decreased to shorten therecording mark and the space. Owing to this, the recording capacity ofan information recording layer of, for example, a 12 cm optical disc canbe increased from 25 GB up to 33.3 GB.

Also according to the present invention, in order to select a mostlikely signal sequence from the waveform of the reproduction signal, ahigher order PRML system is adopted. Specifically, a PR12221ML system isused to reproduce information recorded on an information recordingmedium.

When a high order PRML system is adopted, the evaluation of areproduction signal also needs to be conducted by a higher order method,for the following reasons. As the recording density of the informationrecording medium is improved, recording marks and spaces which areshorter than the resolution of the detection system appear. Fordetermining the recording quality of the information recording medium, apositional shift of a recording mark itself and a positional shift of aspace itself, namely, a positional shift of a set of at least onerecording mark and at least one space needs to be considered, inaddition to a positional shift between a recording mark and a space. Forsuch positional shifts, a pattern including a plurality of edges isdetected. For example, in the case of a positional shift of a recordingmark itself, there is a space at the start and the end of the recordingmark, and so the leading edge and the trailing edge are detected at thesame time. In the case of a positional shift of a set of one mark andone space, for example, “recording mark A-space B”, another space andanother mark are present adjacent to the mark and the space, as “spaceA-mark A-space B-mark B”. Therefore, a total of three edges aredetected.

With the conventional PR1221mL system, it is considered to evaluate therecording quality when one edge is detected in order to evaluate theedge position of the reproduction signal. With the PR12221ML system, therecording quality when a pattern including a plurality of edge shifts isdetected as described above needs to be evaluated. According to thepresent invention, the edge position of the reproduction signal isevaluated using, as an index, the MLSE (Maximum Likelihood SequenceError) disclosed in the U.S. patent application Ser. No. 11/964,825 andthe International Publication No. 2008/081820 A1 pamphlet assigned tothe same assignee as the present application. The entire disclosure ofthe U.S. patent application Ser. No. 11/964,825 is incorporated hereinby reference.

First, with reference to FIG. 6 and FIG. 7, PR12221ML will be brieflydescribed. FIG. 6 is a state transition diagram showing a statetransition rule defined by the RLL(1,7) recording code and theequalization system PR(1,2,2,2,1). FIG. 7 is a trellis diagramcorresponding to the state transition rule shown in FIG. 6.

By a combination of PR12221ML and RLL(1,7), the number of states in adecoding section is limited to 10, the number of state transition pathsis 16, and the number of reproduction levels are 9.

Referring to the state transition rule of PR12221 shown in FIG. 6, tenstates at a certain time are represented as follows. State S(0,0,0,0) isrepresented as “0, state S(0,0,0,1) is represented as S1, stateS(0,0,1,1) is represented as S2, state S(0,1,1,1) is represented as S3,state S(1,1,1,1) is represented as S4, state S(1,1,1,0) is representedas S5, state S(1,1,0,0) is represented as S6, state S(1,0,0,0) isrepresented as S7, state S(1,0,0,1) is represented as S8, and stateS(0,1,1,0) is represented as S9. “0” or “1” in parentheses represents asignal on the time axis, and represents which state will possibly occurat the next time by a state transition from one state. The trellisdiagram shown in FIG. 7 is obtained by developing this state transitiondiagram along the time axis.

In the state transition of PR12221ML shown in FIG. 7, there are numerousstate transition sequence patterns (state combinations) by which aprescribed state at one time is changed to another prescribed state atthe next time via either one of two state transitions. However, thepatterns which are highly likely to cause an error are limited tospecific patterns which are difficult to be distinguished. Focusing onsuch patterns which are likely to cause an error, the state transitionsequence patterns of PR12221 can be summarized as FIGS. 8, 9 and 10.

In FIGS. 8 through 10, the first column represents the state transition(Sm_(k-9)→Sn_(k)) by which two state transitions which are likely tocause an error are branched and rejoin.

The second column represents the state data sequence (b_(k-1), . . . ,b_(k)) which causes the corresponding state transition. “X” in thedemodulated data sequence represents a bit which is highly likely tocause an error in such data. When the corresponding state transition isdetermined to be an error, the number of X (also the number of !X) isthe number of errors. Among a transition data sequence in which X is 1and a transition data sequence in which X is 0, one corresponds to amost likely first state transition sequence, and the other correspondsto a most likely second state transition sequence. In FIGS. 9 and 10,“!X” represents an inverted bit of X.

From the demodulated data sequences obtained by demodulation performedby a Viterbi decoding section, the most likely first state transitionsequence of causing an error and the most likely second state transitionsequence of causing an error can be extracted by comparing eachdemodulated data sequence and the transition data sequence (X: Don'tcare).

The third column represents the first state transition sequence and thesecond state transition sequence.

The fourth column represents two ideal reproduction waveforms (PRequalization ideal values) after the respective state transitions. Thefifth column represents the square of the Euclidean distance between thetwo ideal signals (square of Euclidean distance between paths).

Among combination patterns of two possible state transitions, FIG. 8shows 18 patterns by which the square of the Euclidean distance betweenthe two possible state transitions is 14. These patterns correspond to aportion of an optical disc medium at which a recording mark is switchedto a space (the leading edge and the trailing edge of the recordingmark). In other words, these patterns are 1-bit edge shift errorpatterns.

As an example, state transition paths from S0(k−5) to S6(k) in the statetransition rule in FIG. 7 will be described. In this case, one path inwhich the recording sequence is changed as “0,0,0,0,1,1,1,0,0” isdetected. Considering that “0” of the reproduction data is a space and“1” of the reproduction data is a mark, this state transition pathcorresponds to a 4T or longer space, a 3T mark, and a 2T or longerspace.

FIG. 11 shows an example of the PR equalization ideal waveforms in therecording sequence shown in FIG. 8. In FIG. 8, “A path waveform” of FIG.11 represents the PR equalization ideal waveform of the recordingsequence. Similarly, FIG. 12 shows an example of the PR equalizationideal waveforms shown in FIG. 9. FIG. 13 shows an example of the PRequalization ideal waveforms shown in FIG. 10.

In FIGS. 11, 12 and 13, the horizontal axis represents the sampling time(sampled at one time unit of the recording sequence), and the verticalaxis represents the reproduction signal level.

As described above, in PR12221ML, there are 9 ideal reproduction signallevels (level 0 through level 8).

In the state transition rule shown in FIG. 7, there is another path fromS0(k−5) to S6(k), in which the recording sequence is changed as“0,0,0,0,0,1,1,0,0”. Considering that “0” of the reproduction data is aspace and “1” of the reproduction data is a mark, this state transitionpath corresponds to a 5T or longer space, a 2T mark, and a 2T or longerspace.

In FIG. 11, “B path waveform” represents the PR equalization idealwaveform of this path. The patterns shown in FIG. 8 corresponding to theEuclidean distance of 14 have a feature of necessarily including onepiece of edge information.

FIG. 9 shows 18 patterns by which the square of the Euclidean distancebetween the two possible state transitions is 12. These patternscorrespond to a shift error of a 2T mark or a 2T space; namely, are2-bit shift error patterns.

As an example, state transition paths from S0(k−7) to S0(k) in the statetransition rule in FIG. 7 will be described. In this case, one path inwhich the recording sequence is changed as “0,0,0,0,1,1,0,0,0,0,0” isdetected. Considering that “0” of the reproduction data is a space and“1” of the reproduction data is a mark, this state transition pathcorresponds to a 4T or longer space, a 2T mark, and a 5T or longerspace. In FIG. 12, “A path waveform” represents the PR equalizationideal waveform of this path.

There is another path in which the recording sequence is changed as“0,0,0,0,0,1,1,0,0,0,0”. Considering that “0” of the reproduction datais a space and “1” of the reproduction data is a mark, this statetransition path corresponds to a 5T or longer space, a 2T mark, and a 4Tor longer space. In FIG. 12, “B path waveform” represents the PRequalization ideal waveform of this path. The patterns shown in FIG. 9corresponding to the Euclidean distance of 12 have a feature ofnecessarily including two pieces of edge information on a 2T rise and a2T fall.

FIG. 10 also shows 18 patterns by which the square of the Euclideandistance between two possible state transitions is 12. These patternscorrespond to a portion at which a 2T mark is continuous to a 2T space;namely, are 3-bit error patterns.

As an example, state transition paths from S0(k−9) to S6(k) in the statetransition rule in FIG. 7 will be described. In this case, one path inwhich the recording sequence is changed as “0,0,0,0,1,1,0,0,1,1,1,0,0”is detected. Considering that “0” of the reproduction data is a spaceand “1” of the reproduction data is a mark, this state transition pathcorresponds to a 4T or longer space, a 2T mark, a 2T space, a 3T mark,and a 2T or longer space. In FIG. 13, “A path waveform” represents thePR equalization ideal waveform of this path.

There is another path in which the recording sequence is changed as“0,0,0,0,0,1,1,0,0,1,1,0,0”. Considering that “0” of the reproductiondata is a space and “1” of the reproduction data is a mark, this statetransition path corresponds to a 5T or longer space, a 2T mark, a 2Tspace, a 2T mark, and a 2T or longer space. In FIG. 13, “B pathwaveform” represents the PR equalization ideal waveform of this path.The patterns shown in FIG. 10 corresponding to the square of theEuclidean distance of 12 have a feature of including at least threepieces of edge information.

FIG. 14 shows a structure of a signal evaluation apparatus forevaluating the quality of a reproduction signal in the case where thereproduction signal is processed using the PR12221ML system. The qualityof the reproduction signal is evaluated by the edge position of therecording mark. In the signal evaluation apparatus shown in FIG. 14,identical elements as those in the recording control apparatus shown inFIG. 3 bear identical reference numerals thereto, and similardescriptions thereof will be omitted. The recording code is the RLL (RunLength Limited) code, which is an RLL (1,7) code.

As shown in FIG. 14, an edge shift detection section 10 includes a14-pattern detection section 701, a 12A-pattern detection section 704and a 12B-pattern detection section 707 for respectively detectingpatterns corresponding to FIG. 8 (14-patterns), FIG. 9 (12A-patterns)and FIG. 10 (12B-patterns); differential metric calculation sections702, 705 and 708 for calculating a metric difference of each pattern;and memory sections 703, 706, and 709 for accumulating and storing apositional shift index of each pattern calculated by the differentialmetric calculation sections. The PR equalization section 8 has afrequency characteristic which is set such that the frequencycharacteristic of the reproduction system is the PR(1,2,2,2,1)equalization characteristic.

The pattern detection sections 701, 704 and 707 compare the transitiondata sequences in FIGS. 8, 9 and 10 with the binary data. When thebinary data matches the transition data sequences in FIGS. 8, 9 and 10,the pattern detection sections 701, 704 and 707 select a most likelyfirst state transition sequence 1 and a most likely second statetransition sequence 2 based on FIGS. 8, 9 and 10.

Based on the selection results, the differential metric calculationsections 702, 705 and 708 calculate a metric, which is a distancebetween an ideal value of each state transition sequence (PRequalization ideal value; see FIGS. 8, 9 and 10) and the digitalreproduction signal, and also calculate a difference between the metricscalculated based on the two state transition matrices. Such a metricdifference has a positive or a negative value, and therefore issubjected to absolute value processing.

Based on the binary data, the pattern detection sections 701, 704 and707 generate a pulse signal to be assigned to each of leading edge andthe trailing edge patterns of the recording mark shown in FIGS. 15, 16and 17, and output the pulse signal to the memory sections 703, 706 and709.

Based on the pulse signal output from the pattern detection sections701, 704 and 707, the memory sections 703, 706 and 709 accumulativelyadd the metric differences obtained by the differential metriccalculation sections 702, 705 and 708 for each pattern shown in FIGS.15, 16 and 17.

Now, the detailed pattern classification in FIGS. 15, 16 and 17 will bedescribed in detail. In FIGS. 15, 16 and 17, symbols M and S representthe time series of marks and spaces shown in FIG. 5. Symbol !2Tmindicates that the recording mark is a mark other than a 2T mark (forexample, is a 3T mark). Similarly, a space other than a 2T space isindicated by !2Ts. Symbol xTm represents a recording mark having anarbitrary length, and symbol xTs represents a space having an arbitrarylength. In the case of the RLL(1,7) recording code, the recording marksand the spaces have a length of 2T through 8T. Each pattern numbercorresponds to the pattern number in FIGS. 8, 9 and 10.

As shown in FIG. 15, by the pattern classification of the 14-detectionpatterns in FIG. 15, one edge shift of one space and one mark isclassified. The “start” of a 14-detection pattern indicates an edgeshift of a mark at time i and a space at time i−1. The “end” of a14-detection pattern indicates an edge shift of a mark at time i and aspace at time i+1.

As shown in FIG. 16, by the pattern classification of the 12A-detectionpatterns, a shift of a 2T mark or a 2T space in a 14-detection patternshown in FIG. 14 is further classified by the mark or space at theimmediately previous time or the immediately subsequent time.

In the “start” of the 12A-detection pattern, a shift of a 2T mark attime i sandwiched between a space at time i−1 and a space at time i+1 isclassified by the length of the space at time i+1, or a shift of a 2Tspace at time i−1 sandwiched between a mark at time i and a mark at timei−2 is classified by the length of the mark at time i−2. In the “end” ofthe 12A-detection pattern, a shift of a 2T mark at time i sandwichedbetween a space at time i−1 and a space at time i+1 is classified by thelength of the space at time i−1, or a shift of a 2T space at time i+1sandwiched between a mark at time i and a mark at time i+2 is classifiedby the length of the mark at time i+2.

By the pattern classification of the 12B-detection patterns shown inFIG. 17, a shift of continuous 2T mark and 2T space in a 12A-detectionpattern shown in FIG. 16 is further classified by the mark or space atthe further immediately previous time or the further immediatelysubsequent time. Specifically, a shift of a 2T mark and a 2T spacelocated in succession and sandwiched between one mark and one space isclassified.

In the “start” of the 12B-detection pattern, a shift of a 2T mark attime i and a 2T space at time i+1 sandwiched between a mark at time i+2and a space at time i−1 is classified by the length of the mark at timei+2, or a shift of a 2T mark at time i−2 and a 2T space at time i+1sandwiched between a space at time i−3 and a mark at time i isclassified by the length of the mark at time i−3.

In the “end” of the 12B-detection pattern, a shift of a 2T mark at timei and a 2T space at time i−1 sandwiched between a space at time i+1 anda mark at time i−2 is classified by the length of the mark at time i−2,or a shift of a 2T space at time i+1 and a 2T mark at time i+2sandwiched between a mark at time i and a space at time i+3 isclassified by the length of the mark at time i+3.

Owing to the apparatus shown in FIG. 14, it is now possible to providean index representing a positional shift of a set of one mark and onespace including three edge shifts, i.e., a shift of the mark itselfincluding two edge shifts and a shift of the space itself, in additionto a positional shift between a mark and a space including one edgeshift.

Thus, when a pattern including a plurality of edge shifts is detected,how the edges are shifted with respect to the most likely path can bedetermined. Accordingly, the recording quality can be evaluated, and apattern having a high error rate can be distinguished.

It should be noted that the present invention is related to a method foradjusting a recording condition for forming a recording mark on aninformation recording medium. The evaluation method of a reproductionsignal is not limited to the above-described method. An index valuecalled SAM (Sequence Amplitude Margin) or any other index value orevaluation method may be used to evaluate the degree of an edge shift,and the edge shift of a recording mark may be adjusted based on theevaluation result.

According to the present invention, the recording condition is adjustedto decrease the edge shift of a recording mark, using an index regardingthe edge shift of the recording mark obtained in the above-describedmanner as the evaluation reference. The edge of a recording mark is theborder between the recording mark and a space. Therefore, by theconventional art, the recording condition is classified in accordancewith the lengths of a recording mark and a space adjacent to the edge asdescribed above with reference to FIG. 4.

By contrast, according to the present invention, the influence of heatwhich is caused when an adjacent recording mark is formed due to thesize decrease of the recording mark is considered. Thus, a recordingparameter is changed in accordance with the length of each of arecording mark as the target of the edge adjustment, an adjacent space,and a recording mark adjacent to the space, or in accordance with thelength of each of a recording mark as the target of the edge adjustmentand spaces sandwiching the recording mark. Hereinafter, embodiments ofan information recording medium and a recording/reproduction apparatus,according to the present invention, capable of adjusting the recordingmethod and recording conditions and thus realizing stable high densityrecording will be described.

Embodiment 1

In this Embodiment, an Information Recording Medium and arecording/reproduction apparatus, according to the present invention,capable of adjusting the recording method and recording conditions andthus realizing stable high density recording will be described. In thefollowing description, a recording pulse condition will be described asa recording condition to be adjusted. Alternatively, a recording powercondition or any other recording parameter may be adjusted. Hereinafter,a condition for controlling the position of a leading edge and atrailing edge of a recording mark will be described. Alternatively, arecording pulse width determined by the leading edge and the trailingedge (for example, Ttop) may be controlled. In this embodiment, aPR12221ML system is used for processing a reproduction signal, and theRLL (Run Length Limited) code such as the RLL(1,7) code is used as arecording code.

<Recording Condition Adjustment Method 1-1 Regarding the Leading Edge>

The recording condition adjustment method 1-1 is regarding a leadingedge and is characterized by the following: where a recording markhaving a leading edge to be adjusted is a first recording mark, therecording condition is classified using a length of the first recordingmark, a length of a first space located adjacently previous to the firstrecording mark and a length of a second recording mark not locatedadjacent to the first recording mark and located adjacent to the firstspace.

FIG. 18 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 1-1. In FIG. 18, a recording mark as thetarget of the recording parameter adjustment is represented by recordingmark M(i) as described above with reference to FIG. 4. The other spacesand recording marks are also represented by the same symbols as above.In FIG. 18, symbol !2Tm in M(i−2) indicates that the recording mark is amark other than a 2T mark (for example, is a 3T mark). Similarly, aspace other than a 2T space is indicated by !2Ts. Symbol xTm indicatesthat it is not necessary to limit the length of the recording mark.Similarly in the following description, symbol xTs indicates that it isnot necessary to limit the length of the space. It is noted that in thecase of the RLL(1,7) code, the length of the recording mark and thespace is 2T through 8T.

Now, symbols different from those in FIG. 4 will be described. In thisembodiment, the representation of the relationship between a recordingmark and a space or a recording mark previous thereto or subsequentthereto in the pattern table is complicated. Therefore, in arepresentation of each pattern, T is added only to the recording markM(i) which is the target of the recording parameter adjustment. Forexample, when the immediately previous space S(i−1) is a 3T space andthe recording mark M(i) is a 2T mark, the pattern is represented aspattern 3s2Tm. A pattern represented in the same manner as in FIG. 4 isprovided with parentheses. Accordingly, pattern 3s2Tm is represented aspattern (3s2Tm). Such symbols are also used in the other pattern tablesused for the other recording condition adjustment methods describedlater.

As shown in the pattern table in FIG. 18, the recording condition isclassified in the same manner as in the conventional pattern table inFIG. 4 in the case where the immediately previous space S(i−1) is aspace other than the shortest space (2Ts), i.e., a 3T or longer space.Only in the case where the immediately previous space is the shortestspace, the pattern representation varies in accordance with the lengthof the mark M(i−1) immediately previous to the shortest space. Namely,in this case, the recording parameter is set differently in accordancewith the difference in the length of the mark immediately previous tothe shortest space.

One reason for this is that when the immediately previous space is theshortest space, the recording mark as the target of the recordingparameter adjustment is most influenced by the heat used for forming arecording mark previous to the immediately previous space. Anotherreason is that the shortest mark is extremely short in high densityrecording. In a recording/reproduction system for BD, the length of theshortest mark and the shortest space is about 149 nm in the case of the25 GB recording, and about 112 nm in the case of the 33.4 GB recording.The size of the beam spot is about 250 nm. In the case of the 33.4 GBrecording, even the pattern 2m2s including the shortest mark and theshortest space in continuation is encompassed in the beam spot. In highdensity recording, as the recording mark length is shorter, theexpansion of the recording mark in the width direction is also extremelyreduced. When the shortest mark is formed, the heat amount accumulatedin the recording film is smallest and so the heat amount given to thenext recording mark is also small. Therefore, in this embodiment, therecording parameter is set differently in accordance with the differencein the length of the mark immediately previous to the shortest space, sothat a more appropriate recording mark can be formed in high densityrecording.

In this embodiment, the length of the immediately previous mark isclassified as the shortest mark 2Tm which is most liable to beinfluenced by the thermal interference or a recording mark of anotherlength !2Tm. This is performed in consideration of the scale of thecircuit having the recording parameter. In the case where the circuitscale can be ignored, it is desirable that 3T or longer marks can beindividually classified.

Especially in the case where the recording mark M(i) is a 3T mark orlonger, when the previous recording mark is the shortest mark 2Tm, therecording condition to be adjusted is a recording condition regardingthe 12B patterns of the transition data sequence shown in FIG. 10 (morestrictly, also including the 12A patterns relating to the 2T continuouspatterns). When the previous recording mark is other than the shortestmark, i.e., !2Tm, the recording condition to be adjusted is a recordingcondition regarding the 12A patterns of the transition data sequence,shown in FIG. 9, which are not related to the 2T continuous patterns.Accordingly, when performing the evaluation using the above-describedMLSE as an index, the 12A patterns (not related to the 2T continuouspatterns) and the 12B patterns (including the 12A patterns relating tothe 2T continuous patterns) can be separately evaluated and therecording conditions for these two types of patterns can beindependently adjusted.

FIG. 19 shows recording pulses corresponding to different recordingparameters regarding the leading edge of a recording mark in the casewhere the immediately previous space is the shortest space. FIG. 19,part (a), shows an NRZI signal of pattern 2m2s2Tm, and FIG. 19, part(b), shows a recording pulse for the NRZI signal of pattern 2m2s2Tm;FIG. 19, part (c), shows an NRZI signal of pattern 4m2s2Tm, and FIG. 19,part (d), shows a recording pulse for the NRZI signal of pattern4m2s2Tm; FIG. 19, part (e), shows an NRZI signal of pattern 2m2s3Tm, andFIG. 19, part (f), shows a recording pulse for the NRZI signal ofpattern 2m2s3Tm; FIG. 19, part (g), shows an NRZI signal of pattern4m2s3Tm, and FIG. 19, part (h), shows a recording pulse for the NRZIsignal of pattern 4m2s3Tm; FIG. 19, part (i), shows an NRZI signal ofpattern 2m2s4Tm, and FIG. 19, part (j), shows a recording pulse for theNRZI signal of pattern 2m2s4Tm; FIG. 19, part (k), shows an NRZI signalof pattern 4m2s4Tm, and FIG. 19, part (l), shows a recording pulse forthe NRZI signal of pattern 4m2s4Tm; FIG. 19, part (m), shows an NRZIsignal of pattern 2m2s5Tm, and FIG. 19, part (n), shows a recordingpulse for the NRZI signal of pattern 2m2s5Tm; and FIG. 19, part (o),shows an NRZI signal of pattern 4m2s5Tm, and FIG. 19, part (p), shows arecording pulse for the NRZI signal of pattern 4m2s5Tm.

The recording mark as the target of the recording parameter adjustmentis: in FIG. 19, parts (a) and (c), a 2T mark; in FIG. 19, parts (e) and(g), a 3T mark; in FIG. 19, parts (i) and (k), a 4T mark; and in FIG.19, parts (m) and (o), a 5T mark. The two NRZI signals shown in FIG. 19,parts (a) and (c), indicate that the space immediately previous to therecording mark as the target of the recording parameter adjustment (2Tmark in both cases) is the shortest space in both cases, but the lengthof the recording mark immediately previous to the space is the shortest2T mark in one case and is a mark other than the shortest 2T mark in theother case. Therefore, even for recording the same 2T mark, differentrecording parameters of different recording pulses are set in accordancewith the pattern of the NRZI signal as shown in FIG. 19, parts (b) and(d). In FIG. 19, parts (b) and (d), the recording mark is a 2T mark.Regarding recording marks of other lengths, different recordingparameters are set for different patterns in a similar manner.

Here, the leading edge of the recording mark is adjusted to anappropriate edge position by the recording parameters of the rise edgeposition dTps1 of the first pulse and the fall edge position dTpe1 ofthe first pulse. Therefore, dTps1 and dTpe1 each have a value classifiedin accordance with the pattern table shown in FIG. 18. Namely, there area table of dTps1 and a table of dTpe1. In this embodiment, the leadingedge of the recording mark is adjusted by the recording parameters ofdTps1 and dTpe1. Alternatively, only the position of the rise edgeposition dTps1 of the first pulse may be changed.

<Recording Condition Adjustment Method 1-2 Regarding the Leading Edge>

The recording condition adjustment method 1-2 is also regarding aleading edge and is characterized by the following: in the case wherethe previous mark is the shortest mark in the adjustment method 1-1, therecording parameter is classified by the length of a space immediatelyprevious to the previous mark. Namely, where a recording mark having aleading edge to be adjusted is a first recording mark, the recordingcondition is classified using a length of the first recording mark, alength of a first space located adjacently previous to the firstrecording mark, a length of a second recording mark not located adjacentto the first recording mark and located adjacent to the first space, anda second space located adjacent neither to the first recording mark northe first space and located adjacent to the second recording mark.

FIG. 20 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 1-2. In FIG. 20, the patterns framed by thethick line is expanded with respect to FIG. 18. The patterns in theexpanded part will be described.

As shown in FIG. 20, according to the recording condition adjustmentmethod 1-2, in the case where the previous recording mark M(i−2) is theshortest mark, the recording parameter is set differently in accordancewith the length of the space S(i−3) immediately previous to the shortestmark. Specifically, the recording parameter is set differently inaccordance with whether the length of the space S(i−3) is 2T or not.Owing to this, for example, in an error that a 2T continuous pattern2m2s located immediately previous to the recording mark M(i) is entirelybit-shifted, different recording parameters can be set for a three 2Tcontinuous pattern of 2s2m2s and for a two 2T continuous pattern of!2s2m2s. Therefore, the recording parameter can be more appropriatelyset for a 2T continuous pattern, and the shift of the 2T continuouspattern, which is the cause of the error, can be decreased.

FIG. 21 shows recording pulses corresponding to different recordingparameters regarding the leading edge of a recording mark in the casewhere the space immediately previous thereto is the shortest space andthe recording mark immediately previous to the shortest space is theshortest mark. FIG. 21, part (a), shows an NRZI signal of pattern2s2m2s2Tm, and FIG. 21, part (b), shows a recording pulse for the NRZIsignal of pattern 2s2m2s2Tm; FIG. 21, part (c), shows an NRZI signal ofpattern 3s2m2s2Tm, and FIG. 21, part (d), shows a recording pulse forthe NRZI signal of pattern 3s2m2s2Tm; FIG. 21, part (e), shows an NRZIsignal of pattern 2s2m2s3Tm, and FIG. 21, part (f), shows a recordingpulse for the NRZI signal of pattern 2s2m2s3Tm; FIG. 21, part (g), showsan NRZI signal of pattern 3s2m2s3Tm, and FIG. 21, part (h), shows arecording pulse for the NRZI signal of pattern 3s2m2s3Tm; FIG. 21, part(i), shows an NRZI signal of pattern 2s2m2s4Tm, and FIG. 21, part (j),shows a recording pulse for the NRZI signal of pattern 2s2m2s4Tm; FIG.21, part (k), shows an NRZI signal of pattern 3s2m2s4Tm, and FIG. 21,part (l), shows a recording pulse for the NRZI signal of pattern3s2m2s4Tm; FIG. 21, part (m), shows an NRZI signal of pattern 2s2m2s5Tm,and FIG. 21, part (n), shows a recording pulse for the NRZI signal ofpattern 2s2m2s5Tm; and FIG. 21, part (o), shows an NRZI signal ofpattern 3s2m2s5Tm, and FIG. 21, part (p), shows a recording pulse forthe NRZI signal of pattern 3s2m2s5Tm.

The recording mark as the target of the recording parameter adjustmentis: in FIG. 21, parts (a) and (c), a 2T mark; in FIG. 21, parts (e) and(g), a 3T mark; in FIG. 21, parts (i) and (k), a 4T mark; and in FIG.21, parts (m) and (o), a 5T mark. The two NRZI signals shown in FIG. 21,parts (a) and (c), indicate that the space immediately previous the 2Tshortest mark which is immediately previous to the recording mark as thetarget of the recording parameter adjustment is the shortest 2T space inone case and is a space other than the shortest 2T space (here, 3Tspace) in the other case. Therefore, even for recording the same 2Tmark, different recording parameters of different recording pulses areset in accordance with the pattern of the NRZI signal as shown in FIG.21, parts (b) and (d). In FIG. 21, parts (b) and (d), the recording markis a 2T mark. Regarding recording marks of other lengths, differentrecording parameters are set for different patterns in a similar manner.

<Recording Condition Adjustment Method 2-1 Regarding the Leading Edge>

The recording condition adjustment method 2-1 is regarding a leadingedge and is characterized by the following: where a recording markhaving a leading edge to be adjusted is a first recording mark, therecording condition is classified using a length of the first recordingmark, a length of a first space located adjacently previous to the firstrecording mark and a length of a second space not located adjacent tothe first space and located adjacent to the first recording mark.

More specifically, when a length of the first recording mark is longerthan a prescribed length, the recording condition is classified using acombination of the length of the first recording mark and the length ofthe first space located adjacently previous to the first recording mark.By contrast, when the length of the first recording mark is equal to orshorter than the prescribed length, the recording condition isclassified using a combination of the length of the first recordingmark, the length of the first space, and the length of the second spacenot located adjacent to the first space and located adjacent to thefirst recording mark.

FIG. 22 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 2-1. As shown in FIG. 22, it is understoodthat the recording condition is classified in the same manner as in theconventional pattern table in FIG. 4 in the case where the recordingmark is a mark other than the shortest mark, i.e., a 3T or longer mark.Only in the case where the recording mark M(i) is the shortest mark, thepattern representation varies in accordance with the length of the spaceS(i+1) immediately subsequent to the shortest mark. Namely, therecording parameter is set differently in accordance with whether thelength of the space immediately subsequent to the shortest mark is 2T ornot. As shown in FIG. 22, in the case where the recording mark M(i) isthe shortest mark, the recording parameter is classified in accordancewith the type of the immediately previous space S(i−1) among four typesof 2T, 3T, 4T and 5T and also in accordance with the type of theimmediately subsequent space S(i+1) among two types of 2T and other than2T. In the case where the recording mark M(i) is 3T or longer, therecording parameter is classified in accordance with the type of theimmediately previous space S(i−1) among four types of 2T, 3T, 4T and 5Tbut is not classified in accordance with the type of the immediatelysubsequent space S(i+1). Therefore, the number of types of the lengthsof the immediately previous space is larger than the number of types ofthe lengths of the immediately subsequent space regardless of the lengthof the recording mark M(i).

As described above, in high density recording, the shortest mark isshorter than the other recording marks. Therefore, even when theimmediately previous space is long, if the immediately subsequent spaceis short, the heat amount generated at the time of forming a recordingmark immediately subsequent to the short space is conducted. Namely,after a recording mark is formed, this formed recording mark is deformedby the influence of the heat generated by the later formation of arecording mark. Generally in this case, the influence of the heat isrelated to the trailing edge of the recording mark. However, in highdensity recording, this also influences the leading edge as well as thetrailing edge because the recording mark is extremely short. Therefore,in this embodiment, the recording parameter is classified by thedifference in the length of the space immediately subsequent to theshortest mark, so that a more appropriate recording mark can be formedin high density recording.

Namely, a recording condition is classified by the length of the firstrecording mark. The recording condition is a parameter for adjusting aposition of the leading edge of the first recording mark. However, therecording condition classified by the length of the first recording markinto at least one category, i.e., a category that the length of thefirst recording mark is equal to or shorter than a prescribed length, isfurther classified into two in accordance with whether the length of thesecond space adjacently subsequent to the first recording mark is equalto or shorter than the prescribed length or longer than the prescribedlength.

In this embodiment, regarding the length of the immediately subsequentspace, the recording condition is classified in accordance with whethersuch a length is the shortest space 2Ts which is most liable to beinfluenced by the thermal conduction or another length, i.e., !2Ts. Thisis performed in consideration of the scale of the circuit having therecording parameter. In the case where the circuit scale can be ignored,it is desirable that 3T or longer spaces can be individually classified.

Especially in the case where the immediately previous space S(i−1) is a3T space or longer, when the immediately subsequent space is theshortest space 2Ts, the recording condition to be adjusted is arecording condition regarding the 12B patterns of the transition datasequence shown in FIG. 10 (more strictly, also including the 12Apatterns relating to the 2T continuous patterns). When the immediatelysubsequent space is other than the shortest space, i.e., !2Ts, therecording condition to be adjusted is a recording condition regardingthe 12A patterns of the transition data sequence, shown in FIG. 9, whichare not related to the 2T continuous patterns. Accordingly, whenperforming the evaluation using the above-described MLSE as an index,the 12A patterns (not related to the 2T continuous patterns) and the 12Bpatterns (including the 12A patterns relating to the 2T continuouspatterns) can be separately evaluated and the recording conditions forthese two types of patterns can be independently adjusted.

FIG. 23 shows recording pulses corresponding to different recordingparameters regarding the leading edge of a shortest mark sandwichedbetween the space immediately previous thereto and the space immediatelysubsequent thereto. FIG. 23, part (a), shows an NRZI signal of pattern2s2Tm2s, and FIG. 23, part (b), shows a recording pulse for the NRZIsignal of pattern 2s2Tm2s; FIG. 23, part (c), shows an NRZI signal ofpattern 2s2Tm4s, and FIG. 23, part (d), shows a recording pulse for theNRZI signal of pattern 2s2Tm4s; FIG. 23, part (e), shows an NRZI signalof pattern 3s2Tm2s, and FIG. 23, part (f), shows a recording pulse forthe NRZI signal of pattern 3s2Tm2s; FIG. 23, part (g), shows an NRZIsignal of pattern 3s2Tm4s, and FIG. 23, part (h), shows a recordingpulse for the NRZI signal of pattern 3s2Tm4s; FIG. 23, part (i), showsan NRZI signal of pattern 4s2Tm2s, and FIG. 23, part (j), shows arecording pulse for the NRZI signal of pattern 4s2Tm2s; FIG. 23, part(k), shows an NRZI signal of pattern 4s2Tm4s, and FIG. 23, part (l),shows a recording pulse for the NRZI signal of pattern 4s2Tm4s; FIG. 23,part (m), shows an NRZI signal of pattern 5s2Tm2s, and FIG. 23, part(n), shows a recording pulse for the NRZI signal of pattern 5s2Tm2s; andFIG. 23, part (o), shows an NRZI signal of pattern 5s2Tm4s, and FIG. 23,part (p), shows a recording pulse for the NRZI signal of pattern5s2Tm4s.

The space immediately previous to the recording mark as the target ofthe recording parameter adjustment is: in FIG. 23, parts (a) and (c), a2T space; in FIG. 23, parts (e) and (g), a 3T space; in FIG. 23, parts(i) and (k), a 4T space; and in FIG. 23, parts (m) and (o), a 5T space.

The two NRZI signals shown in FIG. 23, parts (a) and (c), indicate thatthe space immediately previous to the recording mark as the target ofthe recording parameter adjustment is the shortest space (2T space) inboth cases, but the length of the space immediately subsequent to therecording mark is the 2T shortest space in one case and is a space otherthan the shortest space in the other case. Therefore, even for recordingthe same 2T mark, different recording parameters of different recordingpulses are set in accordance with the pattern of the NRZI signal asshown in FIG. 23, parts (b) and (d).

Here, the leading edge of the recording mark is adjusted to anappropriate edge position by the recording parameters of the rise edgeposition dTps2 of the first pulse and the fall edge position dTpe2 ofthe first pulse. Therefore, dTps2 and dTpe2 each have a value classifiedin accordance with the pattern table shown in FIG. 22. Namely, there area table of dTps2 and a table of dTpe2. In this embodiment, the leadingedge of the recording mark is adjusted by the recording parameters ofdTps2 and dTpe2. Alternatively, only the position of the rise edgeposition dTps2 of the first pulse may be changed.

<Recording Condition Adjustment Method 2-2 Regarding the Leading Edge>

The recording condition adjustment method 2-2 is also regarding aleading edge and is characterized by the following: in the case wherethe immediately subsequent space is the shortest space in the adjustmentmethod 2-1, the recording parameter is classified by the length of arecording mark immediately subsequent to the immediately subsequentspace.

Namely, where a recording mark having a leading edge to be adjusted is afirst recording mark, the recording condition is classified using alength of the first recording mark, a length of a first space locatedadjacently previous to the first recording mark, a length of a secondspace not located adjacent to the first space and located adjacent tothe first recording mark, and a second recording mark located adjacentneither to the first recording mark nor the first space and locatedadjacent to the second space.

FIG. 24 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 2-2. In FIG. 24, the patterns framed by thethick line is expanded with respect to FIG. 22. The patterns in theexpanded part will be described.

As shown in FIG. 24, according to the recording condition adjustmentmethod 2-2, in the case where the immediately subsequent space S(i+1) isthe shortest space, the recording parameter is set differently inaccordance with the length of the recording mark M(i+2) immediatelysubsequent to the shortest space. Specifically, the recording parameteris set differently in accordance with whether the length of theimmediately subsequent recording mark M(i+2) is 2T or not. Owing tothis, for example, in an error that a 2T continuous pattern 2m2s formedof a recording mark M(i) and an immediately subsequent space is entirelybit-shifted, different recording parameters can be set for a three 2Tcontinuous pattern of 2m2s2m and for a two 2T continuous pattern of2m2s!2m. Therefore, the recording parameter can be more appropriatelyset for a 2T continuous pattern, and the shift of the 2T continuouspattern, which is the cause of the error, can be decreased.

FIG. 25 shows recording pulses corresponding to different recordingparameters regarding the leading edge of a shortest mark sandwichedbetween the space immediately previous thereto and the shortest spaceimmediately subsequent thereto. FIG. 25, part (a), shows an NRZI signalof pattern 2s2Tm2s2m, and FIG. 25, part (b), shows a recording pulse forthe NRZI signal of pattern 2s2Tm2s2m; FIG. 25, part (c), shows an NRZIsignal of pattern 2s2Tm2s3m, and FIG. 25, part (d), shows a recordingpulse for the NRZI signal of pattern 2s2Tm2s3m; FIG. 25, part (e), showsan NRZI signal of pattern 3s2Tm2s2m, and FIG. 25, part (f), shows arecording pulse for the NRZI signal of pattern 3s2Tm2s2m; FIG. 25, part(g), shows an NRZI signal of pattern 3s2Tm2s3m, and FIG. 25, part (h),shows a recording pulse for the NRZI signal of pattern 3s2Tm2s3m; FIG.25, part (i), shows an NRZI signal of pattern 4s2Tm2s2m, and FIG. 25,part (j), shows a recording pulse for the NRZI signal of pattern4s2Tm2s2m; FIG. 25, part (k), shows an NRZI signal of pattern 4s2Tm2s3m,and FIG. 25, part (l). shows a recording pulse for the NRZI signal ofpattern 4s2Tm2s3m; FIG. 25, part (m), shows an NRZI signal of pattern5s2Tm2s2m, and FIG. 25, part (n), shows a recording pulse for the NRZIsignal of pattern 5s2Tm2s2m; and FIG. 25, part (o), shows an NRZI signalof pattern 5s2Tm2s3m, and FIG. 25, part (p), shows a recording pulse forthe NRZI signal of pattern 5s2Tm2s3m.

The space immediately previous to the recording mark as the target ofthe recording parameter adjustment is: in FIG. 25, parts (a) and (c), a2T space; in FIG. 25, parts (e) and (g), a 3T space; in FIG. 25, parts(i) and (k), a 4T space; and in FIG. 25, parts (m) and (o), a 5T space.The two NRZI signals shown in FIG. 25, parts (a) and (c), indicate thatthe recording mark subsequent to the recording mark as the target of therecording parameter adjustment is the shortest 2T mark in one case andis a recording mark other than the shortest 2T mark (here, 3T mark) inthe other case.

Therefore, even for recording the same 2T mark, different recordingparameters of different recording pulses are set in accordance with thepattern of the NRZI signal as shown in FIG. 25, parts (b) and (d). InFIG. 25, parts (b) and (d), the space immediately previous the recordingmark as the target of the recording parameter adjustment is a 2T space.Regarding immediately previous spaces of other lengths, differentrecording parameters are set for different patterns in a similar manner.

<Recording Condition Adjustment Method 1-1 Regarding the Trailing Edge>

The recording condition adjustment method 1-1 is regarding a trailingedge and is characterized by the following: where a recording markhaving a trailing edge to be adjusted is a first recording mark, therecording condition is classified using a length of the first recordingmark, a length of a first space located adjacently subsequent to thefirst recording mark and a length of a second recording mark not locatedadjacent to the first recording mark and located adjacent to the firstspace.

FIG. 26 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 1-1. As shown in the pattern table in FIG.26, the recording condition is classified in the same manner as in theconventional pattern table in FIG. 4 in the case where the immediatelysubsequent space S(i+1) is a space other than the shortest space (2T),i.e., a 3T or longer space. Only in the case where the immediatelysubsequent space is the shortest space, the pattern representationvaries in accordance with the length of the mark M(i+2) immediatelysubsequent to the shortest space. Namely, the recording parameter is setdifferently in accordance with the difference in the length of the markimmediately subsequent to the shortest space.

A reason for this is that as in the case where the immediately previousspace is the shortest space, when the immediately subsequent space isthe shortest space, the recording mark as the target of the recordingparameter adjustment is most influenced by the thermal interference.Especially in the case where the recording mark M(i) is a 3T mark orlonger, when the subsequent recording mark is the shortest mark 2Tm, therecording condition to be adjusted is a recording condition regardingthe 12B patterns of the transition data sequence shown in FIG. 10 (morestrictly, also including the 12A patterns relating to the 2T continuouspatterns). When the previous recording mark is other than the shortestmark, i.e., !2Tm, the recording condition to be adjusted is a recordingcondition regarding the 12A patterns of the transition data sequence,shown in FIG. 9, which are not related to the 2T continuous patterns.Accordingly, when performing the evaluation using the above-describedMLSE as an index, the 12A patterns (not related to the 2T continuouspatterns) and the 12B patterns (including the 12A patterns relating tothe 2T continuous patterns) can be separately evaluated and therecording conditions for these two types of patterns can beindependently adjusted.

FIG. 27 shows recording pulses corresponding to different recordingparameters regarding the trailing edge of a recording mark in the casewhere the immediately subsequent space is the shortest space. FIG. 27,part (a), shows an NRZI signal of pattern 2Tm2s2m, and FIG. 27, part(b), shows a recording pulse for the NRZI signal of pattern 2Tm2s2m;FIG. 27, part (c), shows an NRZI signal of pattern 2Tm2s4m, and FIG. 27,part (d), shows a recording pulse for the NRZI signal of pattern2Tm2s4m; FIG. 27, part (e), shows an NRZI signal of pattern 3Tm2s2m, andFIG. 27, part (f), shows a recording pulse for the NRZI signal ofpattern 3Tm2s2m; FIG. 27, part (g), shows an NRZI signal of pattern3Tm2s4m, and FIG. 27, part (h), shows a recording pulse for the NRZIsignal of pattern 3Tm2s4m; FIG. 27, part (i), shows an NRZI signal ofpattern 4Tm2s2m, and FIG. 27, part (j), shows a recording pulse for theNRZI signal of pattern 4Tm2s2m; FIG. 27, part (k), shows an NRZI signalof pattern 4Tm2s4m, and FIG. 27, part (l), shows a recording pulse forthe NRZI signal of pattern 4Tm2s4m; FIG. 27, part (m), shows an NRZIsignal of pattern 5Tm2s2m, and FIG. 27, part (n), shows a recordingpulse for the NRZI signal of pattern 5Tm2s2m; and FIG. 27, part (o),shows an NRZI signal of pattern 5Tm2s4m, and FIG. 27, part (p), shows arecording pulse for the NRZI signal of pattern 5Tm2s4m.

The recording mark as the target of the recording parameter adjustmentis: in FIG. 27, parts (a) and (c), a 2T mark; in FIG. 27, parts (e) and(g), a 3T mark; in FIG. 27, parts (i) and (k), a 4T mark; and in FIG.27, parts (m) and (o), a 5T mark. The two NRZI signals shown in FIG. 27,parts (a) and (c), indicate that the recording mark immediatelysubsequent to the 2T shortest space which is subsequent to the 2T spaceis the shortest 2T mark in one case and is a mark other than theshortest 2T mark (here, 4T mark) in the other case. Therefore, even forrecording the same 2T mark, different recording parameters of differentrecording pulses are set in accordance with the pattern of the NRZIsignal as shown in FIG. 27, parts (b) and (d). In FIG. 27, parts (b) and(d), the recording mark is a 2T mark. Regarding recording marks of otherlengths, different recording parameters are set for different patternsin a similar manner.

Here, the trailing edge of the recording mark is adjusted to anappropriate edge position by the recording parameter of the recordingend position offset dCp1. In this case, the pattern table in FIG. 24includes a table of dCp1. In this embodiment, the trailing edge of therecording mark is adjusted by the recording parameter of dCp1.Alternatively, the fall edge position dLpe of the last pulse (only shownin FIG. 27( b)) may be changed. It is noted that for a 2T mark, which isa mono-pulse, dTpe1 is in a competitive relationship against dTpe2 interms of the pulse setting conditions. Therefore, the fall edge positiondLpe of the pulse is usable only when neither dTpe1 nor dTpe2 is used inmono-pulse recording.

<Recording Condition Method 1-2 Regarding the Trailing Edge>

The recording condition adjustment method 1-2 is also regarding atrailing edge and is characterized by the following: in the case wherethe subsequent mark is the shortest mark in the adjustment method 1-1,the recording parameter is classified by the length of a spaceimmediately subsequent to the subsequent mark. Namely, where a recordingmark having a trailing edge to be adjusted is a first recording mark,the recording condition is classified using a length of the firstrecording mark, a length of a first space located adjacently subsequentto the first recording mark, a length of a second recording mark notlocated adjacent to the first recording mark and located adjacent to thefirst space, and a second space located adjacent neither to the firstrecording mark nor the first space and located adjacent to the secondrecording mark.

FIG. 28 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 1-2. In FIG. 28, the patterns framed by thethick line is expanded with respect to FIG. 26. The patterns in theexpanded part will be described.

As shown in FIG. 28, according to the recording condition adjustmentmethod 1-2, in the case where the subsequent recording mark M(i+2) isthe shortest mark, the recording parameter is set differently inaccordance with the length of the space S(i+3) immediately subsequent tothe shortest mark. Specifically, the recording parameter is setdifferently in accordance with whether the length of the immediatelysubsequent space S(i+3) is 2T or not. Owing to this, for example, in anerror that a 2T continuous pattern 2s2m located immediately subsequentto the recording mark M(i) is entirely bit-shifted, different recordingparameters can be set for a three 2T continuous pattern of 2s2m2s andfor a two 2T continuous pattern of 2s2m!2s. Therefore, the recordingparameter can be more appropriately set for a 2T continuous pattern, andthe shift of the 2T continuous pattern, which is the cause of the error,can be decreased.

FIG. 29 shows recording pulses corresponding to different recordingparameters regarding the trailing edge of a recording mark in the casewhere the space immediately subsequent thereto is the shortest space andthe recording mark immediately subsequent to the shortest space is theshortest mark. FIG. 29, part (a), shows an NRZI signal of pattern2Tm2s2m2s, and FIG. 29, part (b), shows a recording pulse for the NRZIsignal of pattern 2Tm2s2m2s; FIG. 29, part (c), shows an NRZI signal ofpattern 2Tm2s2m3s, and FIG. 29, part (d), shows a recording pulse forthe NRZI signal of pattern 2Tm2s2m3s; FIG. 29, part (e), shows an NRZIsignal of pattern 3Tm2s2m2s, and FIG. 29, part (f), shows a recordingpulse for the NRZI signal of pattern 3Tm2s2m2s; FIG. 29, part (g), showsan NRZI signal of pattern 3Tm2s2m3s, and FIG. 29, part (h), shows arecording pulse for the NRZI signal of pattern 3Tm2s2m3s; FIG. 29, part(i), shows an NRZI signal of pattern 4Tm2s2m2s, and FIG. 29, part (j),shows a recording pulse for the NRZI signal of pattern 4Tm2s2m2s; FIG.29, part (k), shows an NRZI signal of pattern 4Tm2s2m3s, and FIG. 29,part (l), shows a recording pulse for the NRZI signal of pattern4Tm2s2m3s; FIG. 29, part (m), shows an NRZI signal of pattern 5Tm2s2m2s,and FIG. 29, part (n), shows a recording pulse for the NRZI signal ofpattern 5Tm2s2m2s; and FIG. 29, part (o), shows an NRZI signal ofpattern 5Tm2s2m3s, and FIG. 29, part (p), shows a recording pulse forthe NRZI signal of pattern 5Tm2s2m3s.

The recording mark as the target of the recording parameter adjustmentis: in FIG. 29, parts (a) and (c), a 2T mark; in FIG. 29, parts (e) and(g), a 3T mark; in FIG. 29, parts (i) and (k), a 4T mark; and in FIG.29, parts (m) and (o), a 5T mark. The two NRZI signals shown in FIG. 29,parts (a) and (c), indicate that the space immediately subsequent to theshortest mark which is subsequent to the recording mark as the target ofthe recording parameter adjustment is the shortest 2T space in one caseand is a space other than the shortest 2T space (here, 3T space) in theother case. Therefore, even for recording the same 2T mark, differentrecording parameters of different recording pulses are set in accordancewith the pattern of the NRZI signal as shown in FIG. 29, parts (b) and(d). In FIG. 29, parts (b) and (d), the recording mark is a 2T mark.Regarding recording marks of other lengths, different recordingparameters are set for different patterns in a similar manner.

<Recording Condition Adjustment Method 2-1 Regarding the Trailing Edge>

The recording condition adjustment method 2-1 is regarding a trailingedge and is characterized by the following: where a recording markhaving a trailing edge to be adjusted is a first recording mark, therecording condition is classified using a length of the first recordingmark, a length of a first space located adjacently subsequent to thefirst recording mark and a length of a second space not located adjacentto the first space and located adjacent to the first recording mark.

More specifically, when a length of the first recording mark is longerthan a prescribed length, the recording condition is classified using acombination of the length of the first recording mark and the length ofthe first space located adjacently subsequent to the first recordingmark. By contrast, when the length of the first recording mark is equalto or shorter than the prescribed length, the recording condition isclassified using a combination of the length of the first recordingmark, the length of the first space, and the length of the second spacenot located adjacent to the first space and located adjacent to thefirst recording mark.

FIG. 30 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 2-1. As shown in FIG. 30, it is understoodthat the recording condition is classified in the same manner as in theconventional pattern table in FIG. 4 in the case where the recordingmark is a mark other than the shortest mark, i.e., a 3T or longer mark.Only in the case where the recording mark M(i) is the shortest mark, thepattern representation varies in accordance with the length of the spaceS(i−1) immediately previous to the shortest mark. Namely, the recordingparameter is set differently in accordance with whether the length ofthe space immediately previous to the shortest mark is 2T or not. Asshown in FIG. 30, the recording parameter is classified in accordancewith the type of the immediately subsequent space S(i+1) among fourtypes of 2T, 3T, 4T and 5T and also in accordance with the type of theimmediately previous space S(i−1) among two types of 2T and other than2T. In the case where the recording mark M(i) is 3T or longer, therecording parameter is classified in accordance with the type of theimmediately subsequent space S(i+1) among four types of 2T, 3T, 4T and5T but is not classified in accordance with the type of the immediatelyprevious space S(i−1). Therefore, the number of types of the lengths ofthe immediately previous space is larger than the number of types of thelengths of the immediately subsequent space regardless of the length ofthe recording mark M(i).

As described above, in high density recording, the shortest mark isshorter than the other recording marks. Therefore, even when theimmediately subsequent space is long, if the immediately previous spaceis short, the heat amount generated at the time of forming a recordingmark immediately previous to the short space is conducted. Namely, theshortest mark is influenced by the heat generated by the previousformation of a recording mark. Generally in this case, the influence ofthe heat is related to the leading edge of the recording mark. However,in high density recording, this also influences the trailing edge aswell as the leading edge because the recording mark is extremely short.Therefore, in this embodiment, the recording parameter is classified bythe difference in the length of the space immediately previous to theshortest mark, so that a more appropriate recording mark can be formedin high density recording.

Namely, a recording condition is classified by the length of the firstrecording mark. The recording condition is a parameter for adjusting aposition of the trailing edge of the first recording mark. However, therecording condition classified by the length of the first recording markinto at least one category, i.e., a category that the length of thefirst recording mark is equal to or shorter than a prescribed length, isfurther classified into two in accordance with whether the length of thesecond space adjacently previous to the first recording mark is equal toor shorter than the prescribed length or longer than the prescribedlength.

In this embodiment, regarding the length of the immediately previousspace, the recording condition is classified in accordance with whethersuch a length is the shortest space 2Ts which is most liable to beinfluenced by the thermal conduction or another length, i.e., !2Ts. Thisis performed in consideration of the scale of the circuit having therecording parameter. In the case where the circuit scale can be ignored,it is desirable that 3T or longer spaces can be individually classified.

Especially in the case where the immediately subsequent space S(i+1) isa 3T space or longer, when the immediately previous space is theshortest space 2Ts, the recording condition to be adjusted is arecording condition regarding the 12B patterns of the transition datasequence shown in FIG. 10 (more strictly, also including the 12Apatterns relating to the 2T continuous patterns). When the immediatelyprevious space is other than the shortest space, i.e., !2Ts, therecording condition to be adjusted is a recording condition regardingthe 12A patterns of the transition data sequence, shown in FIG. 9, whichare not related to the 2T continuous patterns. Accordingly, whenperforming the evaluation using the above-described MLSE as an index,the 12A patterns (not related to the 2T continuous patterns) and the 12Bpatterns (including the 12A patterns relating to the 2T continuouspatterns) can be separately evaluated and the recording conditions forthese two types of patterns can be independently adjusted.

FIG. 31 shows recording pulses corresponding to different recordingparameters regarding the trailing edge of a shortest mark sandwichedbetween the space immediately previous thereto and the space immediatelysubsequent thereto. FIG. 31, part (a), shows an NRZI signal of pattern2s2Tm2s, and FIG. 31, part (b), shows a recording pulse for the NRZIsignal of pattern 2s2Tm2s; FIG. 31, part (c), shows an NRZI signal ofpattern 4s2Tm2s, and FIG. 31, part (d), shows a recording pulse for theNRZI signal of pattern 4s2Tm2s; FIG. 31, part (e), shows an NRZI signalof pattern 2s2Tm3s, and FIG. 31, part (f), shows a recording pulse forthe NRZI signal of pattern 2s2Tm3s; FIG. 31, part (g), shows an NRZIsignal of pattern 4s2Tm3s, and FIG. 31, part (h), shows a recordingpulse for the NRZI signal of pattern 4s2Tm3s; FIG. 31, part (i), showsan NRZI signal of pattern 2s2Tm4s, and FIG. 31, part (j), shows arecording pulse for the NRZI signal of pattern 2s2Tm4s; FIG. 31, part(k), shows an NRZI signal of pattern 4s2Tm4s, and FIG. 31, part (l),shows a recording pulse for the NRZI signal of pattern 4s2Tm4s; FIG. 31,part (m), shows an NRZI signal of pattern 2s2Tm5s, and FIG. 31, part(n), shows a recording pulse for the NRZI signal of pattern 2s2Tm5s; andFIG. 31, part (o), shows an NRZI signal of pattern 4s2Tm5s, and FIG. 31,part (p), shows a recording pulse for the NRZI signal of pattern4s2Tm5s.

The space immediately subsequent to the recording mark as the target ofthe recording parameter setting is: in FIG. 31, parts (a) and (c), a 2Tspace; in FIG. 31, parts (e) and (g), a 3T space; in FIG. 31, parts (i)and (k), a 4T space; and in FIG. 31, parts (m) and (o), a 5T space.

The two NRZI signals shown in FIG. 31, parts (a) and (c), indicate thatthe space immediately previous to the recording mark as the target ofthe recording parameter adjustment is the shortest space in one case andis a space other than the shortest space (here, 4T space) in the othercase. Therefore, even for recording the same 2T mark, differentrecording parameters of different recording pulses are set in accordancewith the pattern of the NRZI signal as shown in FIG. 31, parts (b) and(d). In FIG. 31, parts (b) and (d), the space immediately subsequent tothe recording mark as the target of the recording parameter adjustmentis a 2T space. Regarding recording immediately subsequent spaces ofother lengths, different recording parameters are set for differentpatterns in a similar manner.

Here, the trailing edge of the recording mark is adjusted to anappropriate edge position by the recording parameter of the recordingend position offset dCp2. In this case, the pattern table in FIG. 28includes a table of dCp2. In this embodiment, the trailing edge of therecording mark is adjusted by the recording parameter of dCp2.Alternatively, the fall edge position dLpe of the last pulse (only shownin FIG. 31( b)) may be changed. It is noted that for a 2T mark, which isa mono-pulse, dTpe1 is in a competitive relationship against dTpe2 interms of the pulse setting conditions. Therefore, the fall edge positiondLpe of the pulse is usable only when neither dTpe1 nor dTpe2 is used inmono-pulse recording.

<Recording Condition Adjustment Method 2-2 Regarding the Trailing Edge>

The recording condition adjustment method 2-2 is also regarding aleading edge and is characterized by the following: in the case wherethe immediately previous space is the shortest space in the adjustmentmethod 2-1, the recording parameter is classified by the length of arecording mark immediately previous to the immediately previous space.

Namely, where a recording mark having a trailing edge to be adjusted isa first recording mark, the recording condition is classified using alength of the first recording mark, a length of a first space locatedadjacently subsequent to the first recording mark, a length of a secondspace not located adjacent to the first space and located adjacent tothe first recording mark, and a second recording mark located adjacentneither to the first recording mark nor the first space and locatedadjacent to the second space.

FIG. 32 provides a recording parameter table which shows a specificclassification method of the recording condition used for the recordingcondition adjustment method 2-2. In FIG. 32, the patterns framed by thethick line is expanded with respect to FIG. 30. The patterns in theexpanded part will be described.

As shown in FIG. 32, according to the recording condition adjustmentmethod 2-2, in the case where the immediately previous space S(i−1) isthe shortest space, the recording parameter is set differently inaccordance with the length of the recording mark M(i−2) immediatelyprevious to the shortest space. Specifically, the recording parameter isset differently in accordance with whether the length of the immediatelyprevious recording mark M(i−2) is 2T or not. Owing to this, for example,in an error that a 2T continuous pattern 2s2m formed of a recording markM(i) and an immediately previous space is entirely bit-shifted,different recording parameters can be set for a three 2T continuouspattern of 2m2s2m and for a two 2T continuous pattern of !2m2s2m.Therefore, the recording parameter can be more appropriately set for a2T continuous pattern, and the shift of the 2T continuous pattern, whichis the cause of the error, can be decreased.

FIG. 33 shows recording pulses corresponding to different recordingparameters regarding the trailing edge of a shortest mark sandwichedbetween the space immediately subsequent thereto and the spaceimmediately previous to the shortest space. FIG. 33, part (a), shows anNRZI signal of pattern 2m2s2Tm2s, and FIG. 33, part (b), shows arecording pulse for the NRZI signal of pattern 2m2s2Tm2s; FIG. 33, part(c), shows an NRZI signal of pattern 3m2s2Tm2s, and FIG. 33, part (d),shows a recording pulse for the NRZI signal of pattern 3m2s2Tm2s; FIG.33, part (e), shows an NRZI signal of pattern 2m2s2Tm3s, and FIG. 33,part (f), shows a recording pulse for the NRZI signal of pattern2m2s2Tm3s; FIG. 33, part (g), shows an NRZI signal of pattern 3m2s2Tm3s,and FIG. 33, part (h), shows a recording pulse for the NRZI signal ofpattern 3m2s2Tm3s; FIG. 33, part (i), shows an NRZI signal of pattern2m2s2Tm4s, and FIG. 33, part (j), shows a recording pulse for the NRZIsignal of pattern 2m2s2Tm4s; FIG. 33, part (k), shows an NRZI signal ofpattern 3m2s2Tm4s, and FIG. 33, part (l), shows a recording pulse forthe NRZI signal of pattern 3m2s2Tm4s; FIG. 33, part (m), shows an NRZIsignal of pattern 2m2s2Tm5s, and FIG. 33, part (n), shows a recordingpulse for the NRZI signal of pattern 2m2s2Tm5s; and FIG. 33, part (o),shows an NRZI signal of pattern 3m2s2Tm5s, and FIG. 33, part (p), showsa recording pulse for the NRZI signal of pattern 3m2s2Tm5s.

The space immediately subsequent to the recording mark as the target ofthe recording parameter adjustment is: in FIG. 33, parts (a) and (c), a2T space; in FIG. 33, parts (e) and (g), a 3T space; in FIG. 33, parts(i) and (k), a 4T space; and in FIG. 33, parts (m) and (o), a 5T space.The two NRZI signals shown in FIG. 33, parts (a) and (c), indicate thatthe recording mark previous to the recording mark as the target of therecording parameter adjustment is the shortest 2T mark in one case andis a recording mark other than the shortest 2T mark (here, 3T mark) inthe other case.

Therefore, even for recording the same 2T mark, different recordingparameters of different recording pulses are set in accordance with thepattern of the NRZI signal as shown in FIG. 33, parts (b) and (d). InFIG. 33, parts (b) and (d), the space immediately subsequent to therecording mark as the target of the recording parameter adjustment is a2T space. Regarding immediately subsequent spaces of other lengths,different recording parameters are set for different patterns in asimilar manner.

As described above, in this embodiment, the recording condition forrecording a data sequence on a track is classified using a combinationof a length of a recording mark as the target of the recording parameteradjustment and a length of a space adjacently previous or subsequentthereto. When the length of the recording mark as the target of therecording parameter adjustment is equal to or shorter than a prescribedlength, the classification is performed also using a length of a spacewhich is adjacently subsequent or previous to the above adjacent space.Therefore, even where the size of the recording mark is extremelydecreased and the recording density of the information recording mediumbecomes high, a recording mark having an appropriate shape can berecorded at an appropriate position at higher precision in considerationof the influence of the heat generated when an adjacent recording markis formed.

Only when the length of the recording mark as a target of the recordingparameter adjustment is equal to or shorter than a prescribed length,the recording condition is classified into a smaller category.Therefore, the classification is not redundant, and the recordingcondition can be adjusted at an appropriate parameter scale. Thus,neither the circuit scale, of the recording apparatus, required for therecording adjustment nor the area for storing the recording parametersis made excessively large, and the time required for the adjustment ofthe recording conditions does not become excessively long.

Embodiment 2

Hereinafter, an embodiment of a recording apparatus, a reproductionapparatus, an evaluation apparatus, a recording method and areproduction method according to the present invention will bedescribed.

FIG. 34 is a block diagram showing a structure of an informationrecording/reproduction apparatus 100 acting as a recording apparatus, areproduction apparatus and an evaluation apparatus. The informationrecording/reproduction apparatus 100 includes a recording controlsection 101 and a reproduction signal processing section 102.

The recording control section 101 includes an optical head 2, arecording pattern generation section 11, a recording compensationsection 12, a laser driving section 13, a recording power settingsection 14, an information recording control section 15, and a recordingcompensation parameter determination section 16. The reproduction signalprocessing section 102 includes an optical head 2, a preamplifiersection 3, an AGC section 4, a waveform equalization section 5, an A/Dconversion section 6, a PLL section 7, a PR equalization section 8, amaximum likelihood decoding section 9, and an edge shift detectionsection 10.

An information recording medium 1 is mounted on the informationrecording/reproduction apparatus 100. The information recording medium 1is used for optical information recording or reproduction, and is, forexample, an optical disc.

The optical head 2 converges laser light which has passed through anobjective lens onto a track of an information recording layer of aninformation recording medium 1. For performing recording, the opticalhead 2 forms a recording mark on the track using laser light of aprescribed recording power. For performing reproduction, the opticalhead 2 receives reflected light obtained by irradiating the track withlaser light of a reproduction power and generates an analog reproductionsignal representing information which is recorded on the informationrecording medium 1. The numerical aperture of the objective lens is 0.7to 0.9, and preferably 0.85. The wavelength of the laser light is 410 nmor shorter, and preferably 405 nm.

The preamplifier section 3 amplifiers the analog reproduction signal ata prescribed gain and outputs the resultant signal to the AGC section 4.The AGC section 4 amplifies the reproduction signal using a presettarget gain such that the reproduction signal output from the A/Dconversion section 6 has a constant level, and outputs the resultantsignal to the waveform equalization section 5.

The waveform equalization section 5 has an LPF characteristic forblocking a high frequency range of the reproduction signal and afiltering characteristic for amplifying a prescribed frequency range ofthe reproduction signal. The waveform equalization section 5 shapes thewaveform of the reproduction signal to a desired characteristic andoutputs the resultant signal to the A/D conversion section 6. The PLLsection 7 generates a reproduction clock synchronized with thewaveform-equalized reproduction signal and outputs the reproductionclock to the A/D conversion section 6.

The A/D conversion section 6 samples the reproduction signal insynchronization with the reproduction clock output from the PLL section7, converts the analog reproduction signal into a digital reproductionsignal, and outputs the digital reproduction signal to the PRequalization section 8, the PLL section 7 and the AGC section 4.

The PR equalization section 8 has a frequency characteristic which isset such that the frequency characteristic of the reproduction system isthe characteristic assumed by the maximum likelihood decoding section 9(for example, the PR(1,2,2,2,1) equalization characteristic). The PRequalization section 8 executes PR equalization processing on thereproduction signal so as to suppress high range noise thereof, andintentionally add inter-symbol interference thereto, and outputs theresultant reproduction signal to the maximum likelihood decoding section9. The PR equalization section 8 may include an FIR (Finite ImpulseResponse) filtering structure, and may adaptively control the tapcoefficient using the LMS (The Least-Mean Square) algorithm (see, “TekioShingo Shori Algorithm (Adaptable Signal processing Algorithm) publishedby Kabushiki Kaisha Baifukan).

The maximum likelihood decoding section 9 is, for example, a Viterbidecoder. The maximum likelihood decoding section 9 decodes thereproduction signal which is PR-equalized by the PR equalization section8 using a maximum likelihood decoding system of estimating a most likelysequence based on the code rule intentionally added in accordance withthe type of the partial response, and outputs binary data. This binarydata is demodulated, and as a result, use data, which is informationrecorded on the information recording medium 1, is reproduced.

The edge shift detection section 10 receives the waveform-shaped digitalreproduction signal output from the PR equalization section 8 and thebinary signal output from the maximum likelihood decoding section 9. Theedge shift detection section 10 compares the transition data sequencesshown in FIGS. 8, 9 and 10 against the binary signal. When the binarysignal matches the transition data sequences shown in FIGS. 8, 9 and 10,the edge shift detection section 10 selects a most likely first statetransition sequence 1 and a most likely second state transition sequence2 based on FIGS. 8, 9 and 10.

Based on the selection results, a metric, which is a distance between anideal value of each state transition sequence (PR equalization idealvalue; see FIGS. 8, 9 and 10) and the digital reproduction signal, iscalculated. Also, a difference between the metrics calculated on the twostate transition matrices is calculated. Finally, based on the binarysignal, the edge shift detection section 10 assigns the metricdifference to each of leading edge/trailing edge patterns of therecording mark, and finds an edge shift of a recording compensationparameter from the optimal value, for each pattern.

The recording compensation parameter determination section 16 classifiesa data sequence including a plurality of recording marks and a pluralityof spaces provided between the plurality of recording marks by datapattern including at least one recording mark and at least one space,and determines the recording condition for each data pattern.

Specifically, the classification is performed using a combination of thelength of a first recording mark and the length of a first space locatedadjacently previous or subsequent to the first recording mark, which areboth included in the data sequence. Then, the classification is furtherperformed using the length of a second recording mark which is notlocated adjacent to the first recording mark and is located adjacent tothe first space. A recording condition is assigned to each classifieddata pattern.

Alternatively, the classification is performed using a combination ofthe length of a first recording mark and the length of a first spacelocated adjacently previous or subsequent to the first recording mark,which are both included in the data sequence. Then, the classificationis further performed using the length of a second space which is notlocated adjacent to the first space and is located adjacent to the firstrecording mark. A recording condition is assigned to each classifieddata pattern.

Namely, the recording compensation parameter determination section 16determines a pattern table of the recording parameters, which are therecording conditions classified by data pattern. The pattern table doesnot need to be determined for each recording operation, and is uniquelydetermined in accordance with the type of the information recordingmedium 1 to which the data is to be recorded, conditions such as therecording speed, for example, 2×, and the PRML system of thereproduction signal processing.

The information recording control section 15 changes the setting of therecording parameter in accordance with the pattern table determined bythe recording compensation parameter determination section 16.

It is noted here that the information recording control section 15determines a position at which the recording parameter setting needs tobe changed, based on the edge shift amount detected by the edge shiftdetection section 10. Therefore, it is desirable that the patternclassification obtained by the edge shift detection section 10 is thesame as the pattern table classification obtained by the recordingcompensation parameter determination section 16.

The recording pattern generation section 11 modulates the information tobe recorded and generates an NRZI signal, which is a data sequence. Therecording compensation section 12 generates a recording pulse sequencein accordance with the NRZI signal based on the recording parameterchanged by the information recording control section 15. The recordingpower setting section 14 sets recording powers including the peak powerPp and bottom power Pbw. The laser driving section 13 controls the laserlight emitting operation of the optical head 2 in accordance with therecording pulse sequence and the recording powers which are set by therecording power setting section 14.

Now, an operation of the information recording/reproduction apparatus100 will be described in detail. As shown in FIG. 34, when theinformation recording medium 1 is mounted, the optical head 2 moves to arecording area for adjusting the recording parameter to the optimalrecording parameter. The recording area is, for example, a recordingarea for adjusting the recording powers and the recording pulse, whichare provided in an innermost zone of the information recording medium.

The recording pattern generation section 11 generates a pattern forrecording adjustment as a data sequence for test recording, and outputsthe pattern to the recording compensation section 12. The informationrecording control section 15 applies initial recording conditions storedinside the recording/reproduction apparatus (for example, on a memory)to the recording conditions of the pattern table determined by therecording compensation pattern determination section 16, and thus setsthe recording parameters of the recording pulse shape and the recordingpowers. The recording conditions may be recorded in the PIC area of theinformation recording medium 1. In this case, information on therecording conditions may be obtained from the information recordingmedium 1 by irradiating the PIC area with laser light and applied to theinitial recording conditions.

The recording compensation section 12 generates a recording pulsesequence having the laser light emitting waveform in accordance with thepattern for the recording adjustment based on the recording pulsewaveform, which is output from the information recording control section15 as the recording parameter.

The recording power setting section 14 sets the recording powersincluding the peak power Pp and the bottom power Pbw in accordance withthe initial recording conditions provided by the information recordingcontrol section 15.

The laser driving section 13 controls the laser light emitting operationof the optical head 2 in accordance with the recording pulse sequencegenerated by the recording compensation section 12 and the recordingpowers which are set by the recording power setting section 14. Then,the laser driving section 13 records the recording data on theinformation recording medium 1.

Next, the information recording/reproduction apparatus 100 reproducesrecording data which has been recorded.

The optical head 2 generates an analog reproduction signal indicatinginformation which is read from the information recording medium 1. Theanalog reproduction signal is amplified and AC-coupled by thepreamplifier section 3 and then is input to the AGC section 4. By theAGC section 4, the gain is adjusted such that the output from thewaveform equalizer 5 on a later stage has a constant amplitude. Theanalog reproduction signal output from the AGC section 4 iswaveform-shaped by the waveform equalizer 5. The waveform-shaped analogreproduction signal is output to an A/D conversion section 6. The A/Dconversion section 6 samples the analog reproduction signal insynchronization with a reproduction clock output from the PLL section 7.The PLL section 7 extracts the reproduction clock from a digitalreproduction signal obtained by the sampling performed by the A/Dconversion section 6.

The digital reproduction signal generated by the sampling performed bythe A/D conversion section 6 is input to the PR equalization section 8.The PR equalization section 8 shapes the waveform of the digitalreproduction signal. The maximum likelihood decoding section 9 performsmaximum likelihood decoding on the waveform-shaped digital reproductionsignal output from the PR equalization section 8 to generate a binarysignal.

The edge shift detection section 10 receives the waveform-shaped digitalreproduction signal output from the PR equalization section 8 and thebinary signal output from the maximum likelihood decoding section 9. Theedge shift detection section 10 also finds an edge shift, which is ashift of the recording compensation parameter from the optimal value.The edge shift is output to the information recording control section15.

Based on the result of comparing the edge shift amount detected by theedge shift detection section 10 and a target amount of the edge shiftstored inside the information recording/reproduction apparatus (forexample, on a memory), the information recording control section 15changes a recording parameter, the setting change of which is determinedas being required, for example, a recording parameter which is differentfrom the target value by more than a prescribed value (for example, anerror of 20%). The target value is desirably 0 because the edge shift isa shift of the recording parameter from the optimal value.

By the above-described operation, the information recording/reproductionapparatus 100 according to this embodiment performs a recordingoperation on the information recording medium 1, detects an edge shiftamount by reproducing the recorded information, and updates and adjuststhe recording condition such that the edge shift amount approaches thetarget value. In this manner, the information recording/reproductionapparatus 100 can optimize the recording condition.

As described in Embodiment 1, the above-described recording operation isperformed in accordance with the pattern table created in considerationof a high-order PRML system. Therefore, the recording is performed inconsideration of edges of a plurality of marks and spaces, instead of anedge shift between one space and one recording mark considered in theconventional art. Hence, in high density recording which requires ahigh-order PRML system, the error rate of the recording information canbe reduced, and thus a more stable recording/reproduction system can beprovided.

In the above embodiment, the information recording/reproductionapparatus including the reproduction signal processing section 102 isused in order to describe the recording/reproduction operation. Thepresent invention is also applicable to an information recordingapparatus including only the recording control section 101 forperforming only recording control.

In the pattern tables in the above embodiment, the recording marks orspaces having a length of 5T or longer are put into one category.Alternatively, the recording marks or spaces having a length of 5Tthrough the maximum length may be set differently from one another.

In the above embodiment, the edge position of the recording pulse isvaried in accordance with the pattern. Alternatively, the entirerecording pulse may be shifted in accordance with the pattern. In thiscase, the recording parameter used for recording adjustment is notnecessary. Therefore, the memory capacity in the informationrecording/reproduction apparatus for storing the recording parameterscan be reduced.

The recording conditions classified in the pattern tables may bedescribed in the information recording medium. In this case, therecording compensation parameter determination section 16 does not needto determine the pattern table for each type of the informationrecording medium or for each recording speed. Therefore, the circuitscale can be reduced. In the case where the optimal recording conditionfor each information recording medium is described in accordance withthe pattern table, the work or time of recording parameter adjustmentcan be reduced.

In the above embodiment, the target value of the edge shift is 0.Alternatively, the edge shift may be set for each type of informationrecording mediums of various manufacturers, for each recording speed, orfor each specific pattern included in the pattern table. The targetvalue is stored, for example, during the production of the informationrecording/reproduction apparatus. By keeping on storing target valuescorresponding to newly developed information recording mediums,compatibility to new information recording mediums is obtained.Therefore, it is desirable to store the target values on rewritablememories. A target value for a new information recording medium can bedetermined by reproducing the recording mark, formed with the optimalrecording parameter, by the information recording/reproduction apparatus100.

In the above embodiment, maximum likelihood decoding is performed usinga state transition rule defined by a code having a shortest mark lengthof 2 and the equalization system PR(1,2,2,2,1). The present invention isnot limited to this.

For example, the present invention is also applicable to a case where acode having a shortest mark length of 2 or 3 and the equalization systemPR(C0, C1, C0) are used, to a case where a code having a shortest marklength of 2 or 3 and the equalization system PR(C0, C1, C1, C0) areused, or to a case where a code having a shortest mark length of 3 andthe equalization system PR(C0, C1, C2, C1, C0) are used. C0, C1 and C2are each an arbitrary positive numeral.

In the above embodiment, detailed classification is performed using onlythe marks and spaces having the shortest length, but the presentinvention is not limited to this. For example, the present invention isapplicable to marks or spaces having the second shortest length, ormarks or spaces having larger lengths, instead of marks having theshortest length.

The information recording medium in the above embodiment is not limitedto an optical disc such as a CD, DVD or BD, and may be a magneto-opticalmedium such as an MO (Magneto-Optical Disc), or an information recordingmedium on which information is stored by changing the length or phase ofthe information in accordance with a polarity interval, by which therecording code (0 or 1) of a digital signal is continuous (suchinformation is a recording mark or a space in the above embodiment).

A part of the recording/reproduction apparatus according to the presentinvention may be produced as a one-chip LSI (semiconductor integratedcircuit) or a partial function thereof as a recording conditionadjustment apparatus, which is for adjusting the recording pulse shapefor recording information on an information recording medium. When apart of the recording/reproduction apparatus is produced as a one-chipLSI, the signal processing time for adjusting the recording parametercan be significantly reduced. Each part of the recording/reproductionapparatus may be independently produced as an LSI.

(Recording Waveform)

In the above embodiment, the write pulse included in the write pulsesequence has a multi-pulse waveform. Alternatively, the write pulse mayhave other waveforms. Hereinafter, with reference to FIGS. 35 through37, the waveforms of write pulse usable in the present inventionincluding the multi-pulse waveform will be described.

Generally speaking, a write operation is performed on an optical disc bymodulating data to be written (user data or source data) following apredetermined modulation rule to generate multiple modulated recordingcode patterns, irradiating the disc with pulsed light beams, and formingrecording marks and spaces, each having a length corresponding to thatof an associated one of the multiple modulated recording code patterns.Hereinafter, three examples will be given to describe on what writewaveforms those pulsed light beams are generated. In each of FIGS. 35through 37, the shortest mark is supposed to have a length of 2T (whereT is one reference cycle time of a reference clock and modulation).However, the shortest mark is not limited to this. In the description onFIG. 1, the length of each of a recording mark and a space is 2T through8T. In FIGS. 35 through 37, the length of 9T is also included. 9T is apattern used as a sync. code (synchronization code sequence).

Usually, for writing data (original source data/pre-modulation binarydata) on a storage medium, data is divided into data of a prescribedsize, and the data divided into the prescribed size is further dividedinto frames of a prescribed length. For each frame, a prescribed sync.code/synchronization code sequence is inserted (frame sync. area). Thedata divided into frames is written as a data code sequence modulated inaccordance with a prescribed modulation rule matching therecording/reproduction signal characteristics of the storage medium(frame data area).

By contrast, to the sync. code/synchronization code sequence insertedbetween the frames, the prescribed modulation rule is not applied.Therefore, the sync. code/synchronization code sequence can include apattern other than the code length restricted by the modulation rule.The sync. code/synchronization code sequence determines the reproductionprocessing timing for reproducing the written data. When, for example,the 1-7 modulation is used as the prescribed modulation rule, the lengthof a mark is limited to 2T to 8T. Therefore, as a pattern included inthe sync. code, 9T, which does not appear by the 1-7 modulation, isused.

<N−1 Strategy>

FIG. 35 illustrates a first type of write waveforms. Each write waveformof this first type has a multi-pulse-type strategy (i.e., includesmultiple pulses), and includes a first pulse (with a width Ttop) to bearranged earlier than any other one of the multiple pulses, a last pulse(with a width Tlp) to be arranged at the very last, and middle pulses(with a width Tmp) interposed between the first and last pulses. Amongthe recording-power-related parameters, Pw represents the recordingpower, Pbw represents the bottom power, Pc represents the cooling power,and Ps (Pe) represents the bias power. More specifically, Ps representsa space power in a write-once disc and Pe represents an erase power in arewritable disc. The recording power Pw is also referred to as the “peakpower Pp”. The bottom power is also represented as Pb.

The write waveform to record the shortest mark (2T) has no last pulse ormiddle pulses. The write waveform to record the second shortest mark(3T) has no middle pulses. The middle pulses start to be included in thewrite waveform to record the third shortest mark (4T). And every timethe length increases by 1T, the number of middle pulses increases byone. This first type of write waveform is partly characterized in that awrite waveform to record an nT mark (where n is a natural number) has(n−1) pulses.

In this case, the various types of parameters may be defined byclassifying the lengths of the recording marks and their adjacent spacesin the following manner. First of all, dTtop and Ttop representing theleading edge position and width of the first pulse may be defined byclassifying the lengths of the recording marks into the three categoriesof “2T”, “3T” and “4T or more” and/or classifying the lengths ofadjacent preceding spaces into the four categories of “2T”, “3T”, “4T”and “5T or more”.

Also, Tlp representing the width of the last pulse may be defined byclassifying the lengths of the recording marks into the two categoriesof “3T” and “4T or more”.

Furthermore, dTs marking the end point of the cooling power level Pc (orthe start point of the bias power level Ps or Pe) may be defined byclassifying the lengths of the recording marks into the three categoriesof “2T”, “3T” and “4T or more”.

<N/2 Strategy>

FIG. 36 illustrates a second type of write waveforms. Each writewaveform of this second type also has a multi-pulse-type strategy. Thewrite waveforms to record the shortest mark (2T) and the second shortestmark (3T) have no last pulse or middle pulses. The write waveforms torecord the third shortest mark (4T) and the fourth shortest mark (5T)have no middle pulses. The middle pulses start to be included in thewrite waveform to record the fifth shortest mark (6T). And every timethe length increases by 2T, the number of middle pulses increases byone. This second type of write waveform is partly characterized in thata write waveform to record an mT mark (where m is a natural number) isthe quotient of (m+2).

In this case, the various types of parameters may be defined byclassifying the lengths of the recording marks in the following manner.First of all, dTtop and Ttop representing the leading edge position andwidth of the first pulse may be defined by classifying the lengths ofthe recording marks into the four categories of “2T”, “3T”, “4T, 6T or8T” and “5T, 7T or 9T”.

Also, dTmp representing the leading edge position of the middle pulsesmay be defined by classifying the lengths of the recording marks intothe two categories of “6T or 8T” and “7T or 9T”. Furthermore, theleading edge position may agree with that of the reference clock pulsein the former category and may shift from that of the reference clockpulse by T/2 in the latter category.

Furthermore, dTlp and Tlp representing the position and width of theleading edge of the last pulse may be defined by classifying the lengthsof the recording marks into the two categories of “4T, 6T or 8T” and“5T, 7T or 9T”. Optionally, the leading edge position dTlp may agreewith that of the reference clock pulse in the former category and mayshift from that of the reference clock pulse by T/2 in the lattercategory.

Furthermore, dTs marking the end point of the cooling power level Pc (orthe start point of the bias power level Ps or Pe) may be defined byclassifying the lengths of the recording marks into the four categoriesof “2T”, “3T”, “4T, 6T or 8T” and “5T, 7T or 9T”.

<Castle Type>

FIG. 37 illustrates a third type of write waveforms. Unlike the firstand second types of write waveforms with the multi-pulse-type strategy,each waveform of this third type is shaped such that the power levelbetween pulses, for which the recording powers Pw are set, does notdecrease to the bottom power Pbw but is maintained at a certainintermediate power level Pm. That is to say, the write waveform of thisthird type has a castle-type strategy, and also is formed of a firstpulse (with a width Ttop) to be arranged at the top, a last pulse (witha width Tlp) to be arranged at the very last, and a middle pulseinterposed between the first and last pulses. Among therecording-power-related parameters, Pw represents the recording power,Pm represents the intermediate power, Pc represents the cooling power,and Ps (Pe) represents the bias power. More specifically, Ps representsa space power in a write-once disc and Pe represents an erase power in arewritable disc.

The write waveform to record the shortest mark (2T) has no last pulse ormiddle pulse. The write waveform to record the second shortest mark (3T)have no last pulse. The last and middle pulses start to be both includedin the write waveform to record the third shortest mark (4T). In eachwrite waveform to make a recording mark of 3T or more, the end point ofthe first pulse agrees with the start point of the middle pulse. And ineach write waveform to make a recording mark of 4T or more, the endpoint of the middle pulse agrees with the start point of the last pulse.

The castle type strategy is available in several shapes; specifically,castle-shape, L-shape and mono pulse-shape. In the castle-shape, thewrite waveform to make a recording mark is formed of only one writepulse and has a shape that includes a first interval that begins withthe leading edge of the write pulse and that defines a first power level(i.e., the recording power Pw), a second interval that begins with theend point of the first interval and that defines a second power level(i.e., the intermediate power Pm) that is lower than the first powerlevel, and a third interval that begins with the end point of the secondinterval and that defines a power level that is higher than the secondpower level but is as high as the first power level (i.e., the recordingpower Pw) or a lower than the first power level. In the L-shape, thewrite waveform has a shape in which the power levels of the third andsecond intervals of the castle-shape are made equal to each other. Inthe mono pulse-shape, the write waveform has a shape in which the powerlevels of the first, second and third intervals of the castle-shape aremade equal to one another.

In the example illustrated in FIG. 37, the power levels of the first andthird intervals are supposed to equal to each other to avoidcomplicating the description overly. Naturally, however, mutuallydifferent levels may be set for these two intervals, too. In any case,in the foregoing description, a portion of this write pulse for whichthe power level of the first interval is defined is referred to as a“first pulse”, another portion of the write pulse for which the powerlevel of the second interval is defined an “middle pulse”, and the otherportion of the write pulse for which the power level of the thirdinterval is defined a “last pulse”. Thus, this naming (i.e., the first,intermediate and last pulses) will be used continuously for the rest ofthe description.

In this case, the various types of parameters may be defined byclassifying the lengths of the recording marks and their adjacent spacesin the following manner. First of all, dTtop and Ttop representing theleading edge position and width of the first pulse may be defined byclassifying the lengths of the recording marks into the three categoriesof “2T”, “3T” and “4T or more” and/or classifying the lengths ofadjacent preceding spaces into the three categories of “2T”, “3T”, and“4T or more”.

Also, Tlp representing the width of the last pulse may be defined byregarding the lengths of the recording marks to be “4T or more”. That isto say, every recording mark including the last pulse and having alength of 4T or more may have the same width.

Furthermore, dTc marking the start point of the cooling power level Pcmay be defined by classifying the lengths of the recording marks intothe three categories of “3T”, “4T” and “5T or more”.

Furthermore, dTs marking the end point of the cooling power level Pc(i.e., the start point of the bias power level Ps or Pe) may be definedby classifying the lengths of the recording marks into the threecategories of “2T”, “3T” and “4T or more”.

The manner of classification of the parameters described regarding theN−1 strategy, N/2 strategy and castle type write pulses usable in thepresent invention is different from the manner of classificationdescribed in the above embodiments for the convenience of explanation.For example, in the above embodiments, the parameters are classified byonly the length of a recording mark, or a combination of only the lengthof a recording mark and the length of a space adjacent thereto. However,the manner of classification in the above embodiments can be preferablycombined with the manner of classification described regarding thewaveforms of the write pulses.

Specifically, as shown in, for example, FIGS. 22 and 23, a recordingparameter for adjusting the leading edge of the recording mark havingthe N−1 strategy, N/2 strategy or castle type write pulse waveform maybe classified by a combination of the length of the recording mark M(i)and the length of a space immediately previous thereto S(i−1). When thelength of M(i) is equal to or shorter than a prescribed length (forexample, is the shortest mark), the recording parameter may be furtherclassified by a combination including the length of a space immediatelysubsequent thereto S(i+1); more specifically, in accordance with whetherS(i+1) is equal to or shorter than a prescribed length (for example, isthe shortest space) or longer than the prescribed length.

Alternatively, as shown in, for example, FIGS. 28 and 29, a recordingparameter for adjusting the trailing edge of the recording mark havingthe N−1 strategy, N/2 strategy or castle type write pulse waveform maybe classified by a combination of the length of the recording mark M(i)and the length of a space immediately subsequent thereto S(i+1). Whenthe length of M(i) is equal to or shorter than a prescribed length (forexample, is the shortest mark), the recording parameter may be furtherclassified by a combination including the length of a space immediatelyprevious thereto S(i−1); more specifically, in accordance with whetherS(i−1) is equal to or shorter than a prescribed length (for example, isthe shortest space) or longer than the prescribed length.

The manner of the classification may be changed in accordance with therecording density (25 GB per layer, or 32 GB and/or 33.4 GB per layer)or the type of the recording medium (write once, rewritable, etc.).

When setting the pulse or the power level, the position and the widththereof may be adjusted by a unit of T/16 in any of the N−1 strategy,N/2 strategy and castle type write pulse waveform. Alternatively, suchadjustment may be done more precisely, i.e., by a unit of T/32. Thisadjustment unit may be changed in accordance with the recording density(25 GB per layer, or 32 GB and/or 33.4 GB per layer) or the type of thestorage medium (write once, rewritable, etc.). As the resolution atwhich the write pulse can be set is smaller, the recording mark can befine-tuned more precisely. Therefore, the resolution at which the writepulse can be set is changed when a higher precision recording adjustmentis desired. By setting the write pulse condition in accordance with theresolution at which the write pulses is set (more preferably, by settingthe write pulse such that the resolution is smaller), a more appropriaterecording mark can be formed.

As for the relation between these types of write waveforms and writingspeeds, it could be said that the N/2 strategy write waveform is moresuitable for high-speed writing than the N−1 strategy write waveform,and that the castle type write waveform is more suitable for high-speedwriting than the N/2 strategy write waveform. This is because the N/2strategy write waveform would require more frequent application of therecording power Pw, i.e., would take a greater total amount of time tomake the pulses rise and fall, than the castle type write waveform, thusdelaying the high-speed processing more significantly. The N−1 strategywrite waveform would require more frequent application of the recordingpower Pw, i.e., would take a greater total amount of time to make thepulses rise and fall, than the N/2 strategy write waveform, thusdelaying the high-speed processing more significantly. Considering thispoint, the writing conditions may be stored on an optical disc in thefollowing manner.

First of all, if writing conditions for a 1× writing speed are stored,parameters about the N−1 strategy write waveform may be stored asindispensable ones but parameters about the second write waveform may bestored optionally, for example. Also, if the writing speed is 1×, thethird write waveform may not be used, for example.

Also, if writing conditions for a 2× writing speed are stored,parameters about the N−1 strategy write waveform may be storedoptionally, parameters about the N/2 strategy write waveform may bestored optionally, and parameters about the castle type write waveformmay be stored optionally, for example. In addition, parameters about atleast one of the N−1 strategy write waveform and the N/2 strategy writewaveform may be stored as indispensable ones, for example.

Furthermore, if writing conditions for a 4× writing speed are stored,parameters about the castle type write waveform may be stored asindispensable ones, for example. Also, if the writing speed is 4×,neither the N−1 strategy write waveform nor the N/2 strategy writewaveform may be used, for example.

Furthermore, if writing conditions for a 6× writing speed are stored,parameters about the castle type write waveform may be stored asindispensable ones, for example. Also, if the writing speed is 6×,neither the N−1 strategy write waveform nor the N/2 strategy writewaveform may be used, for example.

Furthermore, if writing conditions for an 8× or higher writing speed arestored, the same rule as the 4× and 6× writing speeds may be applied,for example. That is to say, parameters about the castle type writewaveform may be stored as indispensable ones. Also, if the writing speedis 6×, neither the N−1 strategy write waveform nor the N/2 strategywrite waveform may be used, for example.

On top of that, when those writing conditions are stored, the contentsto be stored may or may not be the same depending on whether the givendisc is an HTL one (High to Low; having a lower reflectance in itsrecorded portions than in its unrecorded portions) or an LTH one (Low toHigh; having a higher reflectance in its recorded portions than in itsunrecorded portions).

The write pulse condition may be set in accordance with the setting ofthe writing speed (recording linear velocity). When the recording isperformed at a lower writing speed in the same optical conditions, theamount of information per unit area is increased and the recordingdensity is raised. However, when the recording density is raised, therecording mark as the target of the adjustment is more liable to beinfluenced by the heat amount caused by the recording mark previous orsubsequent thereto. For this reason, a more appropriate recording markcan be formed by setting the write pulse condition in accordance withthe setting of the linear velocity (preferably, by setting the writepulse condition such that the linear velocity is lower).

(Blu-Ray Disc)

The present invention is applicable to various storage mediums includingBlu-ray disc (BD) and other format optical discs. Herein, BD will bedescribed in detail. BDs are classified according to the property oftheir recording film into various types. Examples of those various BDsinclude a BD-R (write-once) and a BD-RE (rewritable). And the presentinvention is applicable to any type of BD or an optical disc compliantwith any other standard, no matter whether the storage medium is a ROM(read-only), an R (write-once) or an RE (rewritable). Main opticalconstants and physical formats for Blu-ray Discs are disclosed in“Blu-ray Disc Reader” (published by Ohmsha, Ltd.) and on White Paper atthe website of Blu-ray Disc Association (http://www.blu-raydisc.com),for example.

Specifically, as for a BD, a laser beam with a wavelength ofapproximately 405 nm (which may fall within the range of 400 nm to 410nm supposing the tolerance of errors is ±5 nm with respect to thestandard value of 405 nm) and an objective lens with an NA (numericalaperture) of approximately 0.85 (which may fall within the range of 0.84to 0.86 supposing the tolerance of errors is ±0.01 with respect to thestandard value of 0.85) are used. A BD has a track pitch of about 0.32μm (which may fall within the range of 0.310 to 0.330 μm supposing thetolerance of errors is ±0.010 μm with respect to the standard value of0.320 μm) and has one or two information storage layers. A BD has asingle-sided single-layer or a single-sided dual-layer structure on thelaser beam incident side, and its storage plane or storage layer islocated at a depth of 75 μm to 100 μm as measured from the surface ofthe protective coating of the BD.

A write signal is supposed to be modulated by 17PP modulation technique.Recording marks are supposed to have the shortest mark length of 0.149μm or 0.138 μm (which is the length of a 2T mark, where T is one cycleof a reference clock pulse and a reference period of modulation in asituation where a mark is recorded in accordance with a predeterminedmodulation rule), i.e., a channel bit length T of 74.50 nm or 69.00 nm.The BD has a storage capacity of 25 GB or 27 GB (more exactly, 25.025 GBor 27.020 GB) if it is a single-sided, single-layer disc but has astorage capacity of 50 GB or 54 GB (more exactly, 50.050 GB or 54.040GB) if it is a single-sided, dual-layer disc.

The channel clock frequency is supposed to be 66 MHz (corresponding to achannel bit rate of 66.000 Mbit/s) at a standard BD transfer rate (BD1×), 264 MHz (corresponding to a channel bit rate of 264.000 Mbit/s) atBD 4× transfer rate, 396 MHz (corresponding to a channel bit rate of396.000 Mbit/s) at BD 6× transfer rate, and 528 MHz (corresponding to achannel bit rate of 528.000 Mbit/s) at BD 8× transfer rate.

And the standard linear velocity (which will also be referred to hereinas “reference linear velocity” or “1×”) is supposed to be 4.917 m/sec or4.554 m/sec. The 2×, 4×, 6× and 8× linear velocities are 9.834 m/sec,19.668 m/sec, 29.502 m/sec, and 39.336 m/sec, respectively. A linearvelocity higher than the standard linear velocity is normally a positiveintegral number of times as high as the standard linear velocity. Butthe factor does not have to be an integer but may also be a positivereal number. Optionally, a linear velocity that is lower than thestandard linear velocity (such as a 0.5× linear velocity) may also bedefined.

It should be noted that these parameters are those of single-layer ordual-layer BDs already on the market, which have a storage capacity ofapproximately 25 GB or approximately 27 GB per layer. To furtherincrease the storage capacities of BDs, high-density BDs with a storagecapacity of approximately 32 GB or approximately 33.4 GB per layer andthree- or four-layer BDs have already been researched and developed.Hereinafter, exemplary applications of the present invention to such BDswill be described.

<Structure with Multiple Information Storage Layers>

For example, supposing the optical disc is a single-sided disc, from/onwhich information is read and/or written by having a laser beam incidenton the protective coating (cover layer) side, if two or more informationstorage layers need to be provided, then those multiple informationstorage layers should be arranged between the substrate and theprotective coating. An exemplary structure for such a multilayer disc isshown in FIG. 38. The optical disc shown in FIG. 38 has (n+1)information storage layers 502 (where n is an integer that is more thanzero). Specifically, in this optical disc, a cover layer 501, (n+1)information storage layers (layers Ln through L0) 502, and a substrate500 are stacked in this order on the surface on which a laser beam 200is incident. Also, between each pair of adjacent ones of the (n+1)information storage layers 502, inserted as an optical bufferingmaterial is a spacer layer 503. That is to say, the reference layer L0may be arranged at the deepest level that is located at a predetermineddepth from the light incident surface (i.e., at the greatest distancefrom the light source). Multiple information storage layers L1, L2, . .. and Ln may be stacked one upon the other from over the reference layerL0 toward the light incident surface.

In this case, the depth of the reference layer L0 as measured from thelight incident surface of the multi-layer disc may be equal to the depth(e.g., approximately 0.1 mm) of the only information storage layer of asingle-layer disc as measured from the light incident surface. If thedepth of the deepest layer (i.e., the most distant layer) is constantirrespective of the number of storage layers stacked (i.e., if thedeepest layer of a multilayer disc is located at substantially the samedistance as the only information storage layer of a single-layer disc),compatibility can be ensured in accessing the reference layer, no matterwhether the given disc is a single-layer one or a multilayer one. Inaddition, even if the number of storage layers stacked increases, theinfluence of tilt will hardly increase. This is because although thedeepest layer is affected by tilt most, the depth of the deepest layerof a multilayer disc is approximately the same as that of the onlyinformation storage layer of a single-layer disc, and does not increasein this case even if the number of storage layers stacked is increased.

As for the beam spot moving direction (which will also be referred toherein as a “tracking direction” or a “spiral direction”), the opticaldisc may be either a parallel path type or an opposite path type. In adisc of the parallel path type, the spot goes in the same direction onevery layer, i.e., from some inner radial location toward the outer edgeof the disc or from some outer radial location toward the inner edge ofthe disc on every information storage layer.

On the other hand, in a disc of the opposite path type, the spot movingdirections are changed into the opposite one every time the layers toscan are changed from an information storage layer into an adjacent one.For example, if the spot on the reference layer L0 goes from some innerradial location toward the outer edge (which direction will be simplyreferred to herein as “outward”), then the spot on the informationstorage layer L1 will go from some outer radial location toward theinner edge (which direction will be simply referred to herein as“inward”), the spot on the information storage layer L2 will go outward,and so forth. That is to say, the spot on the information storage layerLm (where m is either zero or an even number) will go outward but thespot on the information storage layer Lm+1 will go inward. Conversely,the spot on the information storage layer Lm (where m is either zero oran even number) will go inward but the spot on the information storagelayer Lm+1 will go outward.

As for the thickness of the protective coating (cover layer), tominimize the influence of spot distortion due to either a decrease infocal length with an increase in numerical aperture NA or the tilt, theprotective coating may have its thickness reduced. A numerical apertureNA is defined to be 0.45 for a CD, 0.65 for a DVD, but approximately0.85 for a BD. For example, if the information storage medium has anoverall thickness of approximately 1.2 mm, the protective coating mayhave a thickness of 10 μm to 200 μm. More specifically, a single-layerdisc may include a transparent protective coating with a thickness ofapproximately 0.1 mm and a substrate with a thickness of approximately1.1 mm. On the other hand, a dual-layer disc may include a protectivecoating with a thickness of approximately 0.075 mm, a spacer layer witha thickness of approximately 0.025 mm and a substrate with a thicknessof approximately 1.1 mm.

<Configurations for Single- to Four-Layer Discs>

FIGS. 39, 40, 41 and 42 illustrate exemplary configurations forsingle-layer, dual-layer, three-layer and four-layer discs,respectively. As described above, if the distance from the lightincident surface to the reference layer L0 is supposed to be constant,each of these discs may a total disc thickness of approximately 1.2 mm(but is more preferably 1.40 mm or less if there is a label printed) andthe substrate 500 may have a thickness of approximately 1.1 mm. That iswhy the distance from the light incident surface to the reference layerL0 will be approximately 0.1 mm. In the single-layer disc shown in FIG.39 (i.e., if n=0 in FIG. 38), the cover layer 5011 has a thickness ofapproximately 0.1 mm. In the dual-layer disc shown in FIG. 40 (i.e., ifn=1 in FIG. 38), the cover layer 5012 has a thickness of approximately0.075 mm and the spacer layer 5032 has a thickness of approximately 0.25mm. And in the three-layer disc shown in FIG. 41 (i.e., if n=2 in FIG.38) and in the four-layer disc shown in FIG. 42 (i.e., if n=3 in FIG.38), the cover layer 5014 and/or the spacer layer 5034 may be eventhinner.

Also, in a recorder/player that uses an optical head including anobjective lens with a high NA, aberrations such as a sphericalaberration to be produced due to the thickness from the light incidentsurface of the disc to the information storage layer will seriouslyaffect the quality of a laser beam to be converged on the informationstorage layer. For that reason, such an apparatus is provided with meansfor correcting such aberrations to be produced due to the thickness.

To eliminate the aberration components such as a spherical aberration tobe produced due to the thickness from the surface of the protectivecoating of an optical information storage medium to the informationstorage layer from/on which information is read or written, theaberration correcting means generates an aberration that will cancel theaberration component that has been produced by each information storagelayer. Such an aberration correcting means is originally designedoptically so as to reduce the aberration with respect to the informationstorage layer of a single-layer structure and also takes into accountthe aberration to be produced when a read/write operation is performedon an information storage medium with a dual-layer structure. Theminimum aberration point designed is defined to be located at a depth ofapproximately 80-90 μm as measured from the surface of the protectivecoating. That is why if a read/write radiation needs to be focused on aninformation storage layer, of which the depth is not equal to theminimum aberration point, then an appropriate aberration correctionvalue should be set for that information storage layer by controllingthe aberration correcting means.

<BD's Physical Structure>

FIG. 43 illustrates the physical structure of an optical disc 510 towhich the present invention is applicable. On the discus-like opticaldisc 510, a lot of tracks 512 are arranged either concentrically orspirally. And each of those tracks 512 is subdivided into a lot ofsectors. As will be described later, data is supposed to be written oneach of those tracks 512 on the basis of a block 513 of a predeterminedsize. The data is actually written on a track as a data sequence,including a plurality of recording marks and a plurality of spacesprovided between the plurality of recording marks, which is obtained bymodulating information to be written.

The optical disc 510 includes a PIC (Permanent Information & Controldata) area 514 and an OPC (Optimum Power Control) area 515 at an innerside. The OPC area 515 is used, before user data is recorded, forperforming test recording to find the conditions such as a recordingpower and a write pulse sequence which are optimum for each informationstorage layer. The OPC area 515 is occasionally referred to as a“calibration area”. In the OPC area 515, test recording is performedalso for adjusting the fluctuations of the recording power or the writepulse sequence which are caused by an individual variance among opticaldisc apparatuses or environmental changes such as rapid temperaturechange, adhesion of stain or dust, or the like. The PIC area 514 is areproduction-only area. In this area, disc management information isstored by modulating the grooves at high speed. As the disc managementinformation, OPC parameters required for finding the optimum recordingpower, write strategy type, recommended values of timing, length, etc.of laser pulse generation (recording conditions described in Embodiments1 and 2), recording linear speed, reproduction power, version No. andthe like are stored.

The optical disc 510 has a greater storage capacity per informationstorage layer than a conventional optical disc (such as a 25 GB BD). Thestorage capacity is increased by increasing the storage linear density,e.g., by shortening the mark length of recording marks to be left on theoptical disc, for example. As used herein, “to increase the storagelinear density” means shortening the channel bit length, which is alength corresponding to one cycle time T of a reference clock signal(i.e., a reference cycle time T of modulation in a situation where marksare recorded by a predetermined modulation rule). The optical disc 510may have multiple information storage layers. In the followingdescription, however, only one information storage layer thereof will bedescribed for convenience sake. In a situation where there are multipleinformation storage layers in the same optical disc, even if the trackshave the same width between the respective information storage layers,the storage linear densities could also be different from one layer toanother by uniformly varying the mark lengths on a layer-by-layer basis.

Each track 512 is divided into a lot of blocks 513 every 64 kB(kilobytes), which is the data storage unit. And those blocks are givensequential block addresses. Each of those blocks 513 is subdivided intothree subblocks, each having a predetermined length. The three subblocksare assigned subblock numbers of 0, 1 and 2 in this order.

<Storage Density>

Hereinafter, the storage density will be described with reference toFIGS. 44, 45, 46 and 47.

FIG. 44 illustrates an example of a 25 GB BD, for which the laser beam200 is supposed to have a wavelength of 405 nm and the objective lens220 is supposed to have a numerical aperture (NA) of 0.85.

As in a DVD, data is also written on the track 512 of a BD as a seriesof marks 520, 521 that are produced as a result of a physical variation.The shortest one of this series of marks will be referred to herein asthe “shortest mark”. In FIG. 44, the mark 521 is the shortest mark.

In a BD with a storage capacity of 25 GB, the shortest mark 521 has aphysical length of 0.149 μm, which is approximately 1/2.7 of theshortest mark of a DVD. And even if the resolution of a laser beam isincreased by changing the parameters of an optical system such as thewavelength (405 nm) and the NA (0.85), this value is still rather closeto the limit of optical resolution, below which recording marks are nolonger recognizable for the light beam.

FIG. 46 illustrates a state where a light beam spot has been formed onthe series of recording marks on the track 512. In a BD, the light beamspot 210 has a diameter of about 0.39 μm, which may vary with parametersof the optical system. If the storage linear density is increasedwithout changing the structures of the optical system, then therecording marks will shrink for the same spot size of the light beamspot 210 and the read resolution will decrease.

On the other hand, FIG. 45 illustrates an example of an optical discwith an even higher storage density than a 25 GB BD. But even for such adisc, the laser beam 200 is also supposed to have a wavelength of 405 nmand the objective lens 220 is also supposed to have a numerical aperture(NA) of 0.85. Among the series of marks 524, 525 of such a disc, theshortest mark 525 has a physical length of 0.1115 μm. Compared to FIG.44, the spot size remains approximately 0.39 μm but both the recordingmarks and the interval between the marks have shrunk. As a result, theread resolution will decrease.

The shorter a recording mark is, the smaller the amplitude of a readsignal to be generated when the recording mark is scanned with a lightbeam. And the amplitude goes zero when the mark length gets equal to thelimit of optical resolution. The inverse number of one period of theserecording marks is called a “spatial frequency” and a relation betweenthe spatial frequency and the signal amplitude is called an “opticaltransfer function (OTF)”. As the spatial frequency rises, the signalamplitude decreases almost linearly. And the readable limit at which theamplitude of the signal goes zero is called an OTF cutoff.

FIG. 47 is a graph showing how the OTF of a BD with a storage capacityof 25 GB changes with the shortest recording mark length. The spatialfrequency of the shortest mark on a BD is approximately 80% of, and israther close to, the OTF cutoff frequency. It can also be seen that aread signal representing the shortest mark has amplitude that is assmall as approximately 10% of the maximum detectable amplitude. Thestorage capacity at which the spatial frequency of the shortest mark ona BD is very close to the OTF cutoff frequency (i.e., the storagecapacity at which the read signal has almost no amplitude) correspondsto approximately 31 GB in a BD. When the frequency of the read signalrepresenting the shortest mark comes close to, or exceeds, the OTFcutoff frequency, the limit of optical resolution may have been reachedor even surpassed for the laser beam. As a result, the read signal comesto have decreased amplitude and the SNR drops steeply.

That is why the high storage density optical disc shown in FIG. 45 wouldhave its storage linear density defined by the frequency of the readsignal representing the shortest mark, which may be in the vicinity ofthe OTF cutoff frequency (i.e., it is lower than, but not significantlylower than, the OTF cutoff frequency) or higher than the OTF cutofffrequency.

FIG. 48 is a graph showing how the signal amplitude changes with thespatial frequency in a situation where the spatial frequency of theshortest mark (2T) is higher than the OTF cutoff frequency and where the2T read signal has zero amplitude. In FIG. 48, the spatial frequency ofthe shortest mark 2T is 1.12 times as high as the OTF cutoff frequency.

<Relation Between Wavelength, NA and Mark Length>

An optical disc with high storage density needs to satisfy the followingrelation between the wavelength, the numerical aperture, and themark/space lengths.

Supposing the shortest mark length is TM nm and the shortest spacelength is TS nm, the sum P of the shortest mark length and the shortestspace length is TM+TS nm. In the case of 17 modulation, P=2T+2T=4T.Using the three parameters of the wavelength λ of the laser beam (whichis 405 nm±5 nm, i.e., in the range of 400 nm to 410 nm), the numericalaperture NA (which is 0.85±0.01, i.e., in the range of 0.84 to 0.86) andthe sum P of the shortest mark length and the shortest space length(where P=2T+2T=4T in the case of 17 modulation, in which the shortestlength is 2T), if the unit length T decreases to the point that theinequality

P≦λ/2NA

is satisfied, then the spatial frequency of the shortest mark exceedsthe OTF cutoff frequency.

If NA=0.85 and λ=405, then the unit length T corresponding to the OTFcutoff frequency is calculated by

T=405/(2×0.85)/4=59.558 nm

Conversely, if P>λ/2NA is satisfied, then the spatial frequency of theshortest mark becomes lower than the OTF cutoff frequency.

As can be seen easily, just by increasing the storage linear density,the SNR would decrease due to the limit of optical resolution. That iswhy if the number of information storage layers per disc were increasedexcessively, then the decrease in SNR might be an impermissible degree,considering the system margin. Particularly around a point where thefrequency of the shortest recording mark exceeds the OTF cutofffrequency, the SNR will start to decrease steeply.

In the foregoing description, the storage linear density has beendescribed by comparing the frequency of the read signal representing theshortest mark to the OTF cutoff frequency. However, if the storagedensity of BDs is further increased, then the storage density (and thestorage linear density and the storage capacity) can be defined based onthe same principle as what has just been described by reference to therelation between the frequency of the read signal representing thesecond shortest mark (or the third shortest mark or an even shorterrecording mark) and the OTF cutoff frequency.

<Storage Density and Number of Layers>

A BD, of which the specifications include a wavelength of 405 m and anumerical aperture of 0.85, may have one of the following storagecapacities per layer. Specifically, if the spatial frequency of theshortest marks is in the vicinity of the OTF cutoff frequency, thestorage capacity could be approximately equal to or higher than 29 GB(such as 29.0 GB±0.5 GB or 29 GB±1 GB), approximately equal to or higherthan 30 GB (such as 30.0 GB±0.5 GB or 30 GB±1 GB), approximately equalto or higher than 31 GB (such as 31.0 GB±0.5 GB or 31 GB±1 GB), orapproximately equal to or higher than 32 GB (such as 32.0 GB±0.5 GB or32 GB±1 GB).

On the other hand, if the spatial frequency of the shortest marks isequal to or higher than the OTF cutoff frequency, the storage capacityper layer could be approximately equal to or higher than 32 GB (such as32.0 GB±0.5 GB or 32 GB±1 GB), approximately equal to or higher than 33GB (such as 33.0 GB±0.5 GB or 33 GB±1 GB), approximately equal to orhigher than 33.3 GB (such as 33.3 GB±0.5 GB or 33.3 GB±1 GB),approximately equal to or higher than 33.4 GB (such as 33.4 GB±0.5 GB or33.4 GB±1 GB), approximately equal to or higher than 34 GB (such as 34.0GB±0.5 GB or 34 GB±1 GB) or approximately equal to or higher than 35 GB(such as 35.0 GB±0.5 GB or 35 GB±1 GB).

In this case, if the storage density per layer is 33.3 GB, an overallstorage capacity of approximately 100 GB (more exactly, 99.9 GB) isrealized by the three storage layers combined. On the other hand, if thestorage density per layer is 33.4 GB, an overall storage capacity thatis more than 100 GB (more exactly, 100.2 GB) is realized by the threestorage layers combined. Such a storage capacity is almost equal to thecapacity in a situation where four storage layers, each having a storagedensity of 25 GB, are provided for a single BD. For example, if thestorage density per layer is 33 GB, the overall storage capacity is33×3=99 GB, which is just 1 GB (or less) smaller than 100 GB. On theother hand, if the storage density per layer is 34 GB, the overallstorage capacity is 34×3=102 GB, which is GB (or less) larger than 100GB. Furthermore, if the storage density per layer is 33.3 GB, theoverall storage capacity is 33.3×3=99.9 GB, which is only 0.1 GB (orless) smaller than 100 GB. And if the storage density per layer is 33.4GB, the overall storage capacity is 33.4×3=100.2 GB, which is just 0.2GB (or less) larger than 100 GB.

It should be noted that if the storage density were increasedsignificantly, then it would be difficult to perform a read operationaccurately because the shortest marks should be read under rather severeconditions. That is why a realistic storage density that would realizean overall storage capacity of 100 GB or more without increasing thestorage density too much would be approximately 33.4 GB per layer.

In this case, the optical disc may have either a four-layer structurewith a storage density of 25 GB per layer or a three-layer structurewith a storage density of 33-34 GB per layer. If the number ofinformation storage layers stacked in a disc is increased, however, theread signal obtained from each of those layers will have decreasedamplitude (or a decreased SNR) and stray layer will also be producedfrom those layers (i.e., the read signal obtained from each informationstorage layer will be affected by a signal obtained from an adjacentlayer). For that reason, if a three-layer disc with a storage density of33-34 GB per layer is adopted instead of a four-layer disc with astorage density of 25 GB per layer, then an overall storage capacity ofapproximately 100 GB will be realized by the smaller number of layers(i.e., three instead of four) with the influence of such stray lightminimized. That is why a disc manufacturer who'd like to realize anoverall storage capacity of approximately 100 GB while minimizing thenumber of information storage layers stacked would prefer a three-layerdisc with a storage density of 33-34 GB per layer. On the other hand, adisc manufacturer who'd like to realize an overall storage capacity ofapproximately 100 GB using the conventional format as it is (i.e., astorage density of 25 GB per layer) could choose a four-layer disc witha storage density of 25 GB per layer. In this manner, manufacturers withdifferent needs could achieve their goals using mutually differentstructures, and, and therefore, are afforded an increased degree offlexibility in disc design.

Alternatively, if the storage density per layer is in the 30-32 GBrange, the overall storage capacity of a three-layer disc will be shortof 100 GB (i.e., approximately 90-96 GB) but that of a four-layer discwill be 120 GB or more. Among other things, if the storage density perlayer is approximately 32 GB, a four-layer disc will have an overallstorage capacity of approximately 128 GB, which is the seventh power oftwo that would be processed easily and conveniently by a computer. Ontop of that, compared to the overall storage capacity of approximately100 GB realized by a three-layer disc, even shortest marks could also beread under less severe conditions.

That is why when the storage density needs to be increased, a number ofdifferent storage densities per layer (such as approximately 32 GB andapproximately 33.4 GB) are preferably offered as multiple options sothat a disc manufacturer can design a disc more flexibly by adopting oneof those multiple storage densities and any number of storage layers inan arbitrary combination. For example, a manufacturer who'd like toincrease the overall storage capacity while minimizing the influence ofmultiple layers stacked is offered an option of making a three-layerdisc with an overall storage capacity of approximately 100 GB bystacking three storage layers with a storage density of 33-34 GB perlayer. On the other hand, a manufacturer who'd like to increase theoverall storage capacity while minimizing the impact on read performanceis offered an option of making a four-layer disc with an overall storagecapacity of approximately 120 GB or more by stacking four storage layerswith a storage density of 30-32 GB per layer.

Whichever of these two structures may be adopted for a BD, the presentinvention is preferably usable for adjusting the recording conditions ofthe recording marks to be written on the BD.

As described above, even when the number of information storage layersis increased, the position of the information storage layer L0 farthestfrom the light incidence surface is not changed. Therefore, as thenumber of the information storage layers is increased, the distancebetween the information storage layers is decreased and the inter-layercrosstalk is increased. As a result, the reproduction signal fluctuateslocally or entirely. This fluctuation does not rely on the length of therecording mark in the same information storage layer. However, as therecording mark is shorter, the influence of the fluctuation increases.For this reason, it is preferable that as the recording mark is shorter,the adjustment precision on the recording mark is higher.

Accordingly, when the present invention is applied to a multi-layer BD,a more appropriate recording mark can be formed by setting the writepulse conditions in accordance with the number of the informationstorage layers or the distance between the information storage layers inthe information storage medium. When the number of the informationstorage layers increases, the reflectance of each information storagelayer needs to be decreased. Therefore, the present invention may beapplied when the reflectance is low.

The write pulse conditions may be set in accordance with the recordingpower setting range used for recording information on the informationstorage layer. The recording power setting range defined by the peakpower or the like can be changed in accordance with the number of theinformation storage layers. The reason for this is that the intensity ofthe laser light to be transmitted through the information storage layersneeds to be changed in accordance with the number of the informationstorage layers. Where the recording is performed at the same speed, asthe recording power increases, the variance in recording is larger dueto the response characteristics of laser. Accordingly, it is preferablethat as the recording power increases, the recording adjustment isperformed at higher precision.

For example, the upper limit of the power value set for an informationstorage medium including two information storage layers can be set to belarger than the upper limit of the power value set for an informationstorage medium including one information storage layer. Similarly, theupper limit of the power value set for an information storage mediumincluding three information storage layers can be set to be larger thanthe upper limit of the power value set for an information storage mediumincluding two information storage layers. The upper limit of the powervalue set for an information storage medium including four informationstorage layers can be set to be larger than the upper limit of the powervalue set for an information storage medium including three informationstorage layers.

Accordingly, when the present invention is applied to a multi-layer BD,a more appropriate recording mark can be formed by setting the writepulse conditions in accordance with the recording power setting range ofthe information storage medium.

INDUSTRIAL APPLICABILITY

The present invention is applicable to various types of recordingmediums, on which a data signal can be recorded by laser light, anelectromagnetic force or the like, for example, DVD-RAM, BD-RE or otherinformation recording mediums; and also to a recording operation orother uses in a recording/reproduction apparatus for performingrecording on or reproduction from the above information recordingmedium, for example, a DVD driver, a DVD recorder, a BD recorder orother apparatuses.

REFERENCE SIGNS LIST

-   1 information recording medium-   2 optical head-   3 preamplifier section-   4 AGC section-   5 waveform equalizer-   6 A/D conversion section-   7 PLL section-   8 PR equalization section-   9 maximum likelihood decoding section-   10 edge shift detection section-   11 recording pattern generation section-   12 recording compensation section-   13 laser driving section-   14 recording power setting section-   15 information recording control section-   16 recording compensation parameter determination section-   100 information recording/reproduction apparatus-   101 recording control section-   102 reproduction signal processing section-   201 peak power-   202 bottom power-   203 cooling power-   204 space power-   205 extinction level-   701, 704 707 pattern detection section-   702, 705, 708 differential metric calculation section-   703, 706, 709 memory section

1. An information recording medium, comprising: a track on which a datasequence including a plurality of recording marks and a plurality ofspaces provided between the plurality of recording marks is recordable;and a recording condition recording area in which a recording conditionfor recording the data sequence on the track is recordable; wherein:where a recording mark which is included in the data sequence and is tobe formed on the track based on the recording condition is a firstrecording mark, when a length of the first recording mark is longer thana prescribed length, the recording condition is classified using acombination of the length of the first recording mark and a length of afirst space located adjacently previous or subsequent to the firstrecording mark, and when the length of the first recording mark is equalto or shorter than the prescribed length, the recording condition isclassified using a combination of the length of the first recordingmark, the length of the first space, and a length of a second space notlocated adjacent to the first space and located adjacent to the firstrecording mark.
 2. The information recording medium of claim 1, whereinthe prescribed length is a length of a shortest recording mark in thedata sequence.
 3. The information recording medium of claim 1, whereinin the classification performed using a combination of the length of thefirst recording mark, the length of the first space, and the length ofthe second space, the number of types of the lengths of the first spaceis larger than the number of types of the lengths of the second space.4. The information recording medium of claim 1, wherein the recordingcondition is a parameter for adjusting a position of a leading edge ofthe first recording mark, and the first space is adjacently previous tothe first recording mark.
 5. The information recording medium of claim1, wherein the recording condition is a parameter for adjusting aposition of a trailing edge of the first recording mark, and the firstspace is adjacently subsequent to the first recording mark.
 6. Areproduction apparatus for reproducing information from the informationrecording medium of claim 1, wherein: the information recording mediumincludes a PIC area for storing disc information on the informationrecording medium; and the reproduction apparatus includes a reproductionsignal processing section for executing at least one of irradiation ofthe PIC area with laser light to reproduce the disc information andirradiation of the track with the laser light to reproduce informationwhich is recorded based on the recording condition.
 7. A recordingapparatus for recording a data sequence, including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks, on an information recording medium based on arecording condition recorded on the information recording medium, therecording apparatus comprising: a reproduction signal processing sectionfor irradiating the information recording medium with laser light toreproduce the recording condition; and a recording control section forrecording information on the information recording medium based on therecording condition; wherein: where a recording mark which is includedin the data sequence and is to be formed on the track based on therecording condition is a first recording mark, when a length of thefirst recording mark is longer than a prescribed length, the recordingcondition is classified using a combination of the length of the firstrecording mark and a length of a first space located adjacently previousor subsequent to the first recording mark; and when the length of thefirst recording mark is equal to or shorter than the prescribed length,the recording condition is classified using a combination of the lengthof the first recording mark, the length of the first space, and a lengthof a second space not located adjacent to the first space and locatedadjacent to the first recording mark.
 8. An evaluation apparatus forevaluating an information recording medium having a recording parameterrecorded thereon, the recording parameter being for recording a datasequence including a plurality of recording marks and a plurality ofspaces provided between the plurality of recording marks; wherein: wherea recording mark which is included in the data sequence and is to beformed on the track based on the recording condition is a firstrecording mark, when a length of the first recording mark is longer thana prescribed length, the recording parameter is classified using acombination of the length of the first recording mark and a length of afirst space located adjacently previous or subsequent to the firstrecording mark, and when the length of the first recording mark is equalto or shorter than the prescribed length, the recording parameter isclassified using a combination of the length of the first recordingmark, the length of the first space, and a length of a second space notlocated adjacent to the first space and located adjacent to the firstrecording mark; and the evaluation apparatus comprises a reproductionsignal processing section for generating a digital signal from a signalreproduced from the information recording medium using a PRML signalprocessing system, decoding a binary signal from the digital signal,calculating a differential metric, which is a difference of thereproduction signal from each of a most likely first state transitionsequence and a most likely second state transition sequence, from thebinary signal and detecting each differential metric as an edge shift,and determining whether or not the information recording medium fulfillsa prescribed quality based on the edge shifts.
 9. Arecording/reproduction apparatus for performing at least one ofreproduction from and recording on an information recording mediumdetermined by the evaluation apparatus of claim 8 as fulfilling theprescribed quality.
 10. An information recording medium which includes arecording condition recording area in which recording conditions arerecordable, and on which a data sequence including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks is recordable; wherein: the recording conditions areclassified by a length of the recording mark; where the recordingconditions are each a parameter for adjusting a position of a leadingedge of the recording mark, at least one of the recording conditionsclassified by the length of the recording mark is further classifiedinto two in accordance with whether a length of a space adjacentlysubsequent to the recording mark is equal to or shorter than aprescribed length or longer than the prescribed length; and where therecording conditions are each a parameter for adjusting a position of atrailing edge of the recording mark, at least one of the recordingconditions classified by the length of the recording mark is furtherclassified into two in accordance with whether a length of a spaceadjacently previous to the recording mark is equal to or shorter thanthe prescribed length or longer than the prescribed length.
 11. Areproduction apparatus for reproducing information from the informationrecording medium of claim 10, wherein: the information recording mediumincludes a PIC area for storing disc information on the informationrecording medium; and the reproduction apparatus includes a reproductionsignal processing section for executing at least one of irradiation ofthe PIC area with laser light to reproduce the disc information andirradiation of the track with the laser light to reproduce informationwhich is recorded based on the recording condition.
 12. A recordingapparatus for recording a data sequence, including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks, on an information recording medium based on arecording condition recorded on the information recording medium, therecording apparatus comprising: a reproduction signal processing sectionfor irradiating the information recording medium with laser light toreproduce the recording condition; and a recording control section forrecording information on the information recording medium based on therecording condition; wherein: the recording conditions are classified bya length of the recording mark; where the recording conditions are eacha parameter for adjusting a position of a leading edge of the recordingmark, at least one of the recording conditions classified by the lengthof the recording mark is further classified into two in accordance withwhether a length of a space adjacently subsequent to the recording markis equal to or shorter than a prescribed length or longer than theprescribed length; and where the recording conditions are each aparameter for adjusting a position of a trailing edge of the recordingmark, at least one of the recording conditions classified by the lengthof the recording mark is further classified into two in accordance withwhether a length of a space adjacently previous to the recording mark isequal to or shorter than the prescribed length or longer than theprescribed length.
 13. An evaluation apparatus for evaluating aninformation recording medium having recording conditions recordedthereon, the recording conditions being for recording a data sequenceincluding a plurality of recording marks and a plurality of spacesprovided between the plurality of recording marks; wherein: therecording conditions are classified by a length of the recording mark;where recording conditions are each a parameter for adjusting a positionof a leading edge of the recording mark, at least one of the recordingconditions classified by the length of the recording mark is furtherclassified into two in accordance with whether a length of a spaceadjacently subsequent to the recording mark is equal to or shorter thana prescribed length or longer than the prescribed length; where therecording conditions are each a parameter for adjusting a position of atrailing edge of the recording mark, at least one of the recordingconditions classified by the length of the recording mark is furtherclassified into two in accordance with whether a length of a spaceadjacently previous to the recording mark is equal to or shorter thanthe prescribed length or longer than the prescribed length; and theevaluation apparatus comprises a reproduction signal processing sectionfor generating a digital signal from a signal reproduced from theinformation recording medium using a PRML signal processing system,decoding a binary signal from the digital signal, calculating adifferential metric, which is a difference of the reproduction signalfrom each of a most likely first state transition sequence and a mostlikely second state transition sequence, from the binary signal anddetecting each differential metric as an edge shift, and determiningwhether or not the information recording medium fulfills a prescribedquality based on the edge shifts.
 14. A recording/reproduction apparatusfor performing at least one of reproduction from and recording on aninformation recording medium determined by the evaluation apparatus ofclaim 13 as fulfilling the prescribed quality.
 15. An informationrecording medium, comprising: a track on which a data sequence includinga plurality of recording marks and a plurality of spaces providedbetween the plurality of recording marks is recordable; and at least oneof a PIC area in which a recording condition for recording the datasequence on the track is recorded, and wobbling of the track by whichthe recording condition is recorded; wherein: the recording conditionincludes a parameter for adjusting a position of a trailing end of acooling pulse in a recording pulse waveform for forming the recordingmark; and the parameter is classified using a combination of a length ofthe recording mark and a length of a space located adjacently previousor subsequent to the recording mark.
 16. A reproduction apparatus forreproducing information from the information recording medium of claim15, the reproduction apparatus comprising a reproduction signalprocessing section for executing at least one of irradiation of the PICarea with laser light to reproduce disc information and irradiation ofthe track with the laser light to reproduce information which isrecorded based on the recording condition.
 17. A recording apparatus forrecording a data sequence, including a plurality of recording marks anda plurality of spaces provided between the plurality of recording marks,on an information recording medium based on a recording conditionrecorded on the information recording medium, the recording apparatuscomprising: a reproduction signal processing section for irradiating theinformation recording medium with laser light to reproduce the recordingcondition; and a recording control section for recording information onthe information recording medium based on the recording condition;wherein: the recording condition includes a parameter for adjusting aposition of a trailing end of a cooling pulse in a recording pulsewaveform for forming the recording mark; and the parameter is classifiedusing a combination of a length of the recording mark and a length of aspace located adjacently previous or subsequent to the recording mark.18. An evaluation apparatus for evaluating an information recordingmedium having a recording parameter recorded thereon, the recordingparameter being for recording a data sequence including a plurality ofrecording marks and a plurality of spaces provided between the pluralityof recording marks; wherein: the recording condition includes aparameter for adjusting a position of a trailing end of a cooling pulsein a recording pulse waveform for forming the recording mark; theparameter is classified using a combination of a length of the recordingmark and a length of a space located adjacently previous or subsequentto the recording mark; and the evaluation apparatus comprises areproduction signal processing section for generating a digital signalfrom a signal reproduced from the information recording medium using aPRML signal processing system, decoding a binary signal from the digitalsignal, calculating a differential metric, which is a difference of thereproduction signal from each of a most likely first state transitionsequence and a most likely second state transition sequence, from thebinary signal and detecting each differential metric as an edge shift,and determining whether or not the information recording medium fulfillsa prescribed quality based on the edge shifts.
 19. Arecording/reproduction apparatus for performing at least one ofreproduction from and recording on an information recording mediumdetermined by the evaluation apparatus of claim 18 as fulfilling theprescribed quality.